Max fitment will be 275 on an 8" wheel with 4-1/2" back spacing...
from what I've been told. I will be upgrading to this combo myself in the next few weeks.

Right now on my E-body I have a 255 on an 8" wheel with 3-3/4" backspacing and is too close to fender.

http://www.cuda-challenger.com/cc/index.php?topic=19470.0