Max rear tire size
 

Wondering if anyone knows the max rear tire size I can fit on my 74 running the factory wheels (15”)

I have 275 /60/15 on rear of mine

I would pick a tire manufacturer and size and see if their fitment chart recommends the tire size on a 8" wide wheel.
If my 245-60-15 BFG's were any wider I would have to move the parking brake bracket.

I run 255/60-VR15's all the way around on my '73. 255/60-15's became an optional tire in '78 on the factory 8" wheel. The only issue I've seen is minor rubbing, at full lock on the left front tire. It touches the head of one of the "carriage" style bolts that hold the steering box to the frame and keeps it polished for me. :D

No issues on the rear at all.

https://cimg1.ibsrv.net/gimg/www.cor...c76e4a162e.jpg

Good luck... GUSTO

I have 295 50/15's on the 8" rallys, but I also have offset trailing arms (68 Vert)

I run 275-60-15's on the rear of mine but I did relocate the parking brake bracket, from the side, to the top of the T/A.