How much fender and leaf clearance is needed?

Probably looks real good with the 275s.

I bought the tires and rims for the new rear 8 3/4 rear end, they will fit, I measured everything like crazy and found that with the new rear end dimensions 255s would clear with some extra room to be safe.

I just kinda lucked out to find that they fit with the 7 1/4. I am still making up my mind if I want to modify the fender lip. I think rolling them would be okay, but I changed my mind about cutting them.