Changing '69 Dart SBP to BBP

in that case, i would do what Doug said, find a BBP rear end that matches yours (if you switch from an 7.25 to and 8.25 you would need to shorten your drive shaft)

the for the front, you can use a set of spindles from a B body (i believe) and use their brakes, or use a set of 72-up A body discs (also from the spindle out)