Rim and tire size

[427TJ]

What you should do first is jack the car up, remove the rear wheel(s) and start measuring. Measure the distance from the outer face of the brake drum (where the wheel rests when mounted) to the vertical face of the inner wheelwell. That's the critical number and will guide your backspace decision. Take the tire size you think you're going to use into account too. Tire cross-section could eat-into that distance. Do the math carefully and you'll probably have to measure it a few times while you crunch the numbers.

Another method wold be to mount a wheel with a known backspace and measure from the outer rim edge. Again, factor-in tire cross-section.

Depending on the tire size you could run out of room if rim backspace goes deeper than about 3.75 to 4.0 inches. That's just from my own experience on two of my '67s. Perhaps you can ask a tech guy at a wheel manufacturer and see what his fitment guide says.