255 60 15 1968 barracuda

With SBP axles I think a 15x7 with 4.25” of backspace would be the ticket, 4.5” would put you right on the springs. If you had BBP axles then 4.5” would work, BBP axles move the axle flange further out.
Sorry to ask a dumb question but what does SBP & BBP refer to? I assume they have something to do with the rear axle assembly.