76 breaks problem

In '76, factory front disc brakes were 5x4.5 bolt pattern. The factory did not mix'n'match different bolt patterns on the same vehicle, front to rear. With front disc brakes, the only way you could have 5x4 in the rear is if somebody swapped in a different differential. But, I see you have the same wheels all the way around on your car. So if all your wheels (and therefore the bolt circle) are the same, then you either have non-'76 front disc brakes (either '72 and earlier Kelsey/Hayes, or aftermarket), or you are measuring your bolt circle incorrectly and have a 4.5" bolt circle. Look at @Dana67Dart 's picture above, and how he is measuring the bolt circle- the outside of a stud/hole to the center of a stud/ hole across from it; his picture shows he is measuring a 4" bolt circle drum, and not a 4.5". Are you SURE this is what you have, and how you arrived at it? Both patterns were available in '76, but not together. 4 wheel drum cars got 4", cars with factory front discs got 4.5".