Joe, would 5" backspace work on both front and rear or should front be less? Thanks
If you run 8" wheels on all four corners, 5" bs would work fine and allow you the luxury of freequent tire rotations. Should front be less? only if you want the most tire patch you can get at all four corners. Mixing wheel width and BS front to rear is done frequently on these cars.
As stated above, less BS on a 9" rear wheel can, may , might, maybe not ??? cause rubbing on the outer quarter lip. however, you could roll or cut the outer lip to correct)?
You also can get away with less BS and a wider rear wheel if you are at normal ride height, run a lower aspect ratio tire, and not planning to lower the suspension.
Keep in mind, you cant add to backspacing to a wheel , but you can remove it with wheel spacers (if you get it wrong by a small amount). if you dont get enough BS, you have to modify the outer wheel well to clear outer interference. if you get too much BS, you can add spacers to clear the inner interference. (either way not ideal but the latter is easier).
if it were me and assuming they fit (cant be sure without knowing the mods to the car ):
5.5 BS rear w/ 265 @ 35 tire on 9" wheel
5.0 BS front w/245 or 235 @ 35 to 40 tire on 8" wheel.
all depends what you want the car to do?