Yep, same wheel tubs and quarters.
So factory wheels should work for you if you stick with a 225/60/15 or smaller, 225's will be tight on the quarter lips. If you want to go with bigger tires, you'll need to add backspace. Your '68 B 8 3/4 is about 2.3" wider than an A-body 8 3/4 with BBP axles, so, you can add ~1.15" of backspace to whatever someone with an A-body 8 3/4 runs. For a 15x8 and a BBP A-body 8 3/4 you usually want ~4.5" of backspace, for example.
With your '68 B 8 3/4, for a 15x8 and say 275's you'd want ~5.65" of backspace as long as the springs are in the stock location (43" c-c on the perches). If you kept the B-body perches at 44" c-c, you won't be able to run that much backspace, or 275's.
