A rear end from any F, J or M body will fit, but they were offered in both 7.25" and 8.25". Personally, I would never put another 7.25" axle under it, they are easy to break. I'd get an 8.25" which will bolt right in but requires the driveshaft be shortened a bit. Axle ratios will vary. Most V8 cars had a terrible 2.2 gear (especially 1980 and later) though cop 318-4 cars would have a 2.9 gear. Slant 6 cars usually had a 2.7 or 2.9 gear. There was also less common 2.4 and 3.2 gears. I'd never put a 2.2 or 2.4 gear behind a slant 6 if that's what you've got.