On my 68 Barracuda,
The factory tubs have no problems at all running 275s on 8.5s on the stock 8.75 rear end, lowered or not.
The offset shackles allow the tires to be moved inboard far enough to rub on the inner walls of the tubs, so there is no point in moving the springs any further, until the tubs are modified..
I have moved the springs that far, and had no trouble with the fuel tank.
My pipes are 3 in/3 out, and while the tailpipes are a tightfit, mine don't actually hit anything, even after I lowered the car.
With the springs moved, my factory tubs accepted 295/50-15s on 10" rims, with no problems. With just a lil hammerring in all the right spots, those same tubs accepted 325/50-15s also on 10s. My car is lowered, so it was tight, and I had to slow down for the turns............
I narrowed the rear so that I could run standard 4.5bs wheels.
