Don't know if this will help, but I run a 255/70/15 on an 8" wide rim on the rear of my 54-3100. On the front I run a 235/70/15 on a 7" wide rim. These are 5 lug 15" rims 4-3/4" bolt patterns as I have added discs to the front and run a Camaro rear end. The original widths remain 62" wide, mounting flange to mounting flange. All four rims have a backspacing of 4". They are centered in the wheel wells and I have experienced not clearance issues. The 255 is 28.5" tall and the 235 is 27" tall. This, along with 50 year old springs gives the truck a slight rake to the front. BTW...I prefer the BF Goodrich T/A series tire.
I found that there were more rim backspacing options in the 15" size. The backspacing determines how far in or out the tire runs in the wheelwell. Normally, you want to run the same diameter rims 15's,16's etc. front and back so you only have to carry one spare.
Thinking down the road....the 15" 5 lug disc conversion uses Camaro rotors and calipers and over-the-counter wheel bearings while the 6 lug conversion uses the stock GM hubs, a more expensive set of bearings that you will more than likely have to mail-order. The 5 lug 4-3/4" conversion will fit the 15" rim.
Now that you are aware that the sizes (width) of tire that will fit your truck you need to see if you can find a 16" or 17" rim with 4" of backspacing that gives you the "look" you're after. I wanted a tire that would "fill" the wheel well and not look like a little donut because I am retaining the stock ride height.
I might suggest that you check a Summit or Jegs catalog to see which manufacturers offer what backspacing in the diameter you decide to run. If you're going to try to go the salvage yard route, you need to brush up on how to measure "back-spacing"....arm yourself with a tape measure, make sure you're looking at the correct lug spacing (GM vs the others), and plan on spending some quality time hunting.
I spent a good deal of time researching rim diameters and tire combinations and suggest you use the "search" feature in this site to become familiar with the terminology. Also suggest you work out a plan for your truck so that down the road you aren't saddled with a bunch of parts that you can't use on future upgrades. After all....that's the fun part of working on old iron.
I've got some pictures in my webshots album that might help you visualize what you do or do not want. Hope this helps!
