Newbie with some questions

Now is a good time to consider new studs, and while you are changing the studs, get longer ones and change over to all right hand thread. Studs weaken and break, so it is time, based on the age and possibly some unknown abuse. Think safety.

New studs is a good idea, never can be too safe! So basically whatever tire is close to same size ( I'm thinking a 215/75R16 or a 215/65R17 or if the 225 worked that might be nice) but what's got me a little confused is rim sizing. I'm assuming I can use my same hubs just have to get the offset rim or do I need to offset the rim and add a spacer to clear the spindle? forgive me i'm a slow learner! I am leaning towards adding disc brakes to the front at least, maybe leave the backs as drums unless there's a good option for them. saw in another tread about a bolt on front disc brake package that looked interesting but this is a whole different topic but probably a good one to ask experiences on as well while i'm at it I guess!

Forgive me if I cause confusion. The spacer is an Idea, it is not necessary if you get the proper back spacing. As for what size of rim, What fits over your drums without causing problems. That includes the Disk brakes if you put them on. As was stated, keeping the same diameter as the originals, will keep your speedo reading as close to accurate as possible with out changing that. Look for the right combination that works for the looks and carry capacity you need. You are a smart person, and can figure what works best for you and what you want. Always good to get Ideas, just do what you want and need.

From the chart on tirerack.com:
29" diameter tires will result from 205R16, 235/70R16, 255/60/R17, 255/55R18, 205/80R16, 255/70R15, 255/65R16, 235/75R16, LT23575R15
Each of those tires will require a different width wheel relative to the aspect ratio. Look on the tire mfg. websites and see what wheel width each tire requires. Most will give a range of widths. Or talk to a tire store and they can give you the widths from their catalogs.

I know I indicated that I put on 225/65R17 on my front and implied it was 29" dia. I was incorrect in that I see it is 28.52" diameter. The tire itself is 8.86" wide and I put it on a 7" wide wheel. However, the front doesn't have to be exactly the same diameter as the rear if you are going the street rod route. If you are going the stock route, all 4 tires being the same size is best and that way your spare will be the same for all 4 locations.

One of the things that I had a situation with on our R120 was clearing the tie-rod ends. My R120 situation may not be like any other because I changed over to DANA Axles for 4X4. Tha being said, the citprod ends will still be there on a solid axle and should be taken into consideration for the clearance situation.
The auto recyclers have lots of really nice alloy wheels and many of them look cracker on these old trucks. It is like dressing up your Grandmother and putting some makeup on her. Just for fun, my son popped a JEEP TJ Wrangler alloy wheel on his L110 before we reduced the Binder to bits. Very nice, I think. But then, I am a little strange most of the time.
On my son's L110 we are using Dana 44 axels adapted to 2010 Dodge Ram 3500 17 inch wheels with 265-70 R17 BFG all terrain tires. The truck will look like a steam roller with Cummins 4bta power
BTW, I like a taller wheel, say 16 or 17 then use a LT tire to add more rubber to fill those big fenders up just a little. Matching the OEM speedo would be my last concern. depending on how good the speedometer is, it could be just about anywhere. A good GPS is easy to afford and accurate. This is a good way to check your speedo then adjust your speed. If you keep the OEM speedo, give it a little light oil where the shaft/cable goes in the back. This may be the first hug it has ever had.