.....I'd say with a 235 on a 15x8 you'd want a minimum of 5" of backspace, 5.25" would be better. You can go with more backspace than that too (probably up to about 6.25" of backspace), but the TTII's don't come with more than 5.25" of backspace in a 15x8. If it's a '65-67 than a 15x8 with a 5" backspace should be a piece of cake, and anything up to about 6" of backspace on a 15x8 would be fine.
I have a '68-70 B rear in my Duster. I run 18x10's with a 7" backspace and 295/35/18's, although I also added a 1/2" spring offset kit when I converted mine (perches at 42"c-c) and trimmed the outer quarter lip a little to squeeze the 295's into the stock wheelhouse.
