I have 4.75" back space. they are a little close for me, and will rub a little on the inside wheelwell if I corner it to fast. 90% of the time they dont rub and I am not concerned about it. I think 4.5" would be perfect, I may try a 1/4" spacer and see if it helps. The passenger wheelwell is bigger than the drivers side wheelwell. I guess that is just 1968 quality control.