Scarebird and Wilwood offer disk conversions for either 9" or 10" front drum spindle/hub that keep the SBP wheels. If you change to BBP 5 x 4.5", your spare tire won't fit both front and rear unless you go big at the rear. But then, many new cars today don't even provide a spare (call a tow truck). The Dr Diff kit (and others) change the whole front spindle, hub, and ball joints to a factory 1973+ BBP front disk setup.