Father-Son 1974 Duster Project
Here is the comparison between 245 and 275 width tires.
And yes everything is stock location. The tub size is no the problem. The problem is an 8-1/4 A-Body rear is an inch narrower than an 8-3/4 A-Body rear. So the spring hitting the side of the tire is the problem. My wheels only come with 4-1/2 backspace. They are Summit Racing knockoff (practically exact copies) of Weld Prostar wheels. The Weld wheels come in 2-1/2, 3-1/2 and 4-1/2 backspace. The 8” Weld wheel with 3-1/2 backspace and a 275/60/15 is probably a safe bet. The summit racing wheels are returnable even if you put a tire on them to check out fitment. But if you mount a tire on the well wheel which is close to 400 bucks you bought it and it can’t be returned
Here is the comparison between 245 and 275 width tires.