On your wheel choice. I’ve done a ton of measuring and testing to find what works in fitting a 15” Cragar SS under a 69 Firebird with a factory BOP rear end (a bit wider than a Chevy rear) and stock hight springs. Cragar only offers one backspace these days, 4.25”. On a 15x8 SS rim, even a 245 TA radial gets pushed into the outer wheel well to cut up the tire, leaving lots of space wasted on the inside between the tire and the spring. So after driving the tire shop crazy with mounting and remounting different sized tires I went the direction of the backspacing. With a brand new set of 15x8 Cragar SS rims I had the welds cut and the “barrel” moved inward an additional 1and 7/8”. Then mounted a 255 15 GoodYear TA radial. Fits very well, no rubbing inside or out. Probably could have gone wider but the size works very well. I think I paid $180 per rim. That may seem like a lot but not really when you figure how long you’re going to be looking at it, and how high you’ll have to lift your car to fit that 10” rim to clear, ruining the stance of a classic car IMHO. Also, avoid comparing with what fits on our friends 67s and 68s, the 69 is one of a kind.