The limitation is mostly the springs. The nice thing about the B body rear (65-70) is that with a 1" spring relocation kit you can bolt one right in. I've seen people with this relocation and rear go as wide as 305's in the back, so, it allows for quite a bit more tire. On the other hand, if you move the perches on the e-body rear you'd still get the spring clearance you'd need, you'd just have to run a rim with a little more backspace. Which might be a good thing, since most modern rims have more backspacing than the e-body's used stock.