A simple coversion....

How many times I have heard "if I can't find X I'll just.... What seams like a simple change can get to be big. Can't find brake drums, so an axle swap. Those that do these Like MM or Nikki know it is anything but simple to make it work like it should. There are U joint, track width, pinion angle, brakes and brake lines, spring perches and the list goes on.
I purchased a running "core" engine for one of my cabovers. I came from a late 70's IHC 4300 and is going in an early 80's 9670. Only a few years difference but I am going to tell the story of just one small area to be converted.
The engine came with brackets for the A/C compressor. It was originally fitted with a York 2 cyl recip, which I find to be troublesome. It vibrates bad and breaks mounting bolts and is impossible to keep the belt tight on. The early 9670's were fitted with the Delco A-6 (one of the best compressors made in my opinion, they were used in all high end car (Jag's, Rolls Royce etc)) Gm stopped making them in the 80s and later 9670's went back to the York.
SO, this is the saga of what has to be changed for such a little thing as an A/C compressor change. Keep in mind, that the engine block has not changed in decades, any small or Big cam will have similar bolt holes available for the swap. So should be "bolt on" conversion
The very nice purpose built brackets are still available new from IHC so were ordered. They aren't supplied with the needed bushings, so off to the hardware store for 2 sizes of bushing stock. The drive pulley diameter on the engines vary (late 70's used a 7" drive early 80's used either an 8 or 9" drive) so the A-6 had to have the smaller pulley on the clutch, the 80's used a 5 3/4" clutch, but the 70's needed a 5" clutch to keep the compressor speed near as possible to the original. The pulleys themselves could be interchanged between the engines, but the later engine uses a two piece acc drive pulley where as the earlier is a one piece, to change you have to pull both parts. Furthermore, changing pulleys would changed the fan drive ratio, so I kept the orignal, and changed the clutch pulley on the A/C instead.
The Air compressor for air brakes is directly behind the acc drive so sit behind the A/C compressor, the 70's engine and later 80's used a two cyl Bendix compressor, where as the early 80's used the single cyl Holset compressor. How the water line to the compressor head is different on each compressor, as is how close the compressor is to the A/C compressor. This ment all water connection had to be re-routed and in one case hose needed to be replace with hard tubing to gain clearance.
The OEM manifold for the A/C compressor is still available so that was ordered. The belt to drive the compressor is now not stock for either application and was measured and purchased by size. Several of the mounting bolts are odd length and had to be cut down from longer bolts.
The belt tensioning "strap" will be made by me in my shop, although the original is likely available from IHC, the cost isn't worth it.
It has taken a lot of time and fab work, but when I am done, it will function like the original and with very few "custom parts" so that things will interchange between my two cabovers.
They point of this long story is: this is a "bolt on" conversion, with factory parts and it still took time and patients to get it right. There is no such thing as "I guess I'll throw a different axle under it" the devil is in the details and the details make or break a job. It can be done, but how well its done is directly related to the time put in. Those that put bodies on other frames have a TON of work to do it well, if they put in the time, they get a result that is worth the effort, but never under estimate the time involved, if you haven't done a ton of them, make your best guess, and double it!
I am still surprised how much time it took to replace one A/C compressor with another, even when most of the parts for either were at hand.

I think you have covered all of the angles on this subject really well, Mister CB89
The first big mistake a person makes may be thinking, "This will be an easy one!" The second mistakes may be being too conservative in estimating the time and money to finish. Never forget the cash thing. This is where relationships break down.
I shy away from frame swaps, probably because I am not familiar with the procedure and I do not want to change my modus operandi. My area of comfort is the axle swap. There is a little more to getting an axle swap right, so just "U" bolting an axle in place is only the first of a few important steps.
My wife likes to play the numbers keeper. She suggests I have more than 3000 hours into our 1940 Ford. The receipts show that the cost of getting it right have topped a hundred grand and this does not include the $24,749.03 for body and paint. I only mention this so if anyone is planning to be invited to Pebble Beach, you had better be prepared to more than double the time and money I have into this Ford.
Do I have any regrets? Yes I do and they are big regrets. I wish I had never got involved with the Ford at this level. I under estimated the time to finish. The money was easier to plan for and I have not had many big money surprises. The events that I had not allowed for was my aging, health issues and the loss of time and some mobility that go with each of those situations. I still get up and get at it most every day. I would rather fall on a screwdriver and die than drop dead in my comfortable office chair.
Tomorrow, I am installing a steering column and wiring it up. See you in the shop by 09:00h.
My original hobby was an IHC truck and a bunch of antique single cylinder engines. KISS. Keep It Simple Stupid

CB, I think LUCK plays into it. I keep various versions of certain parts like IHC driveshafts and IHC wheels.

My "luck" of parts compatibility therefore increases with each added piece in my "collection".

I admire your perseverance on the A/C work and agree that the A-6 is the Cadillac of old A/C compressors.

Nikki, you are so right on the cash thing. The compressor brackets are die case aluminum (2 of them) and run about $80 a piece, the manifold is another $80, the compressor can run anywhere from $50 for a used, in unknown condition to as high as $950 for brand new in the box. Add in miscellaneous hardware and any repairs to the compressor and clutch and the price goes up
I felt the brackets and manifold were worth the price, because I have these on another engine in a truck and know they work well. I could have fab'd up brackets out of steel, but it wouldn't be any better and likely worse than the factory brackets. One very nice feature of the factory system of brackets is the belt can be tensioned without jacking the cab, something not possible with the two cyl recip compressor.
When I repaired the A/C on the cabover I am running now, it had all the brackets and a compressor that had a bad shaft. I replaced the compressor direr and condenser, and it has worked very well. At that time, you could buy a rebuilt compressor (Murry brand rebuild) with clutch from O' realys? for $150 with a $10 core charge. Murry and 4 seasons have a very mixed reputation when it come to rebuilds. I got lucky and have no problem with the compressor. A-6's are getting scarce on the market and the core is now over $50.
I have since started buying "cores" off the internet and going thru them myself. The A-6 doesn't have any "gaskets" but uses O ring making it likely that seal kits will be around for a long time.
One of the things that makes an A-6 so good, is it is assembled with select fit parts, meaning that when you build it, you select from an assortment of parts to get the correct clearances. This can be a problem if the rebuilder just throws them together with an assortment of any old parts. I suspect this is why some rebuilder have a mixed reputation. Fortunately, the A-6 was used in a great number of cars, eve Ford used a GM A-6 in some of their cars. that there are a great number still around. I have also heard that Compressor Works has copied them and making them "new". I search out ones that the shaft can be turned 360 deg and have a complete clutch. Delco clutches are not made any more for this model and most are "rebuilt" meaning someone skimcut the pulley face and re-vulcanized the rubber on the nose. So a good clutch is often worth the cost of the core compressor, if the compressor can be salvaged , then you are money ahead, if not you can break it down for parts.

MM what happened to the pic's of your "car"?