I wanted to ignore the whole wheel offset thing, but thanks. Are you saying that 73 and up BBP stock rims were +.125 offset over the pre 73 SBP rims???
My original 14 x 5.5, 4.50 BC Ralleyes are long gone. I measured what I had and measured the offset from center. Hub surface to inside tire bead. Both factory Ralleye rims. 15 x 6.5, 5 x 4.50 BC offset toward outside .500 inches. 14 x 5.5, 5 x 4.00 BC offset toward outside .375 inches. I did not measure as precisely as you, but I was being careful since I was ordering custom wheels for the 66 Formula S.
