I recently purchased a set of vintage 45's that are 16x8 w 4.5 bs. I have a 68 with 69 style single piston caliper one piece hub/rotors. On the back I run 255/50/16's. They clear, but I do not run the chrome wheel well trim. In the front I have 245/50/16's they barely clear, again I am not running chrome trim. When cycling them through with out the spring I have about a 1/4 inch clearance with a brand new lower control arm bumpstop that it two inches high (uncompressed). These same wheels and tires rubbed on CarlC's 68 camaro, but he runs the chrome trims. My 2cents of advise: If you don't have means to check this out on your car before buying, or you don't want to roll your fenders the largest tire I would run is a 225 on the 16x8 w 4.5 bs. Of course this all changes depending on your track width and what kind of brakes you run.
1968 SS 350 coupe, w/ 406 inches of tremec shifted mouse.