1964 plymouth valiant recommended rim for 245s in the back

6" is about the narrowest you can get away with 245's so i'd start there with a eye toward backspace. like we all stated before, the outer wheel lip and how the quarter pinches in is where you're going to find the limiting factors.

i would think a 7 or 8 would allow the tire to sit a little more "square" and not bulge out the sidewall as much, but i don't know if you've got the real estate for that with an off the shelf rim.