I have 15x8 Vette Ralleys with a 4" back spacing and 255/60/15 BFG's with no problems what so ever. I have also used these same wheels a run a 295/50/15 BFG with no problems on both my 68 and the current 67 that I have.
Yes I have pic's and will send them your way tonight. I am running a 15x5 ralley (from a 65 Caprice) on the front with a 26/7.5/15 Mickey Thompson Sportsman tire. Looks good when I have the trim rings and caps on them.