OldIHC

Anybody have the ratios for 41-49 midsize 4 speed trans? Trying to workout ideal rear gears for comfortable hwy driving.

Well most four speed transmissions are straight through in fourth gear. The rest of the ratios won't matter too much but you can always pull the top cover off and start counting teeth.

Not much help here, but...
That "four speed NON-OD, no-synchro trans) was shared amongst ALL the truck manufacturers.
Yes, top gear is straight through 1:1.
NO compound low that I remember...? I could be wrong...
Reverse lockout lever on some..
My point is that this box was SO common! Just used different input shafts and adaptors for closed driveline, etc. on all the different manufacturers.
Things like the countergear and mainshaft stayed the same.
I'll look online for gear ratios. It's a COMMON box.

Thanks. So a 3.07 rear should be good cruiser gears?

Depends on your tire size, of course.
And whether the engine has any juevos.

There is more to consider here than a wonderful final drive ratio. That old and lazy castiron lump of an engine may not be able to drive a 3:07. It takes lots of energy to push a old truck through the air and as the speed increases it takes more power to push. If this were my truck, I would be looking for a 3:75 or 3:54, maximum.
Lest say that your old IHC engine will push your truck to a steady 60 MPH and very suddenly and without warning the brakes have to stop you and the truck, the brakes will likely fail because the design was not able to handle the conversion of inertia into heat and dissipate the heat. This is brake failure and the point where your insurance company will walk away and leave you with the cost of making it right, for those you come in contact with.

Yes, well to imply that these huge brakes wont be able to stop this insanely light truck from 60 mph, is just silly. Anyway, back to the topic at hand. Turns out ive got 3.73s in it, but the motor is wound tight at 40 mph, which leads me to the conclusion that the 4th gear in this is nowhere near 1 to 1. Is it possible that some of these trans were lower geared to compensate for the 2 speed rear? Anyone have any definitive ratios?

Sincerely doubt you have 3.73's more likely double that. Sitting on 20" rubber 3.73 would top out well over 80 at 3,000 rpm.
Drop the driveshaft, and look on the pinion head for the gear count, then you will KNOW what you have. Low 6's to 8's are common for 2 spds.
Stock KS-5 ratios are 5.13, 5.83 and 6.33 (all in high) My KS-7 has 6.14

Top gear is 1:1 it is your rear ratio that is off! If you came up with 3.73 by counting driveshaft revolutions with one wheel off the ground, you did it wrong! It will be double with one wheel stationary. Numbers stamped on the head of the pinion don't lie nor are they overly optimistic, they are what you have!

My factory service manual lists only one standard issue transmission available for K, KB-5 trucks, H-41-B

ratios: first (low) 6.40-1
second 3.09-1
third 1.69-1
fourth 1.00-1

there are other transmissions available special order, their ratios are same/very similar, all end in fourth being 1.00-1,

except F-52-B, F-52-C, F-54-B, FF-54-B, which all these are five speed with fifth being direct 1.00-1 rather than fifth gear = overdrive.

Rear axles available for K, KB-5 include R-1360, R2360-2 speed,

standard R-1360 ratio is 6.16-1, optional ratios for R-1360 include 5.28-1, and 6.66-1

standard R-2360 2 speed ratios, 5.83-1/8.11-1, optional ratios include 5.14-1/7.15-1, and 6.33-1/8.81-1

this is of course assuming your truck still has original from factory running gear in it,

every 4 speed transmission International lists fourth is 1.00-1,

there is zero chance that big ol dually rear axle is 3.73-1, best you have is optional 5.28-1, most likely have standard 6.16-1,

truck was made to haul stuff, not do a Tokyo drift around the curves,

you can either install a gearvendor overdrive unit, or swap a modern axle from some 1970s up truck,

You can put in a newer transmission, but fourth will still be 1.00-1, you can put in a fifth overdrive, but you won't gain much in the long run with that low rear axle ratio as most fifth overdrive aren't much over, the 5 speed in my KB-6 fifth is .823-1