I have 255/60/15's on 8" wheels with 4" backspacing on my '74 Cuda, and I had to modify my fenders to keep from rubbing. They rubbed on the very bottom of the front of the wheel opening. 245/60/15 with 4.5" backspacing might work without fender modifications, but I don't know for sure.

Do you have any pictures of your fender modifications?