Somebody changed more than the backing pates, shoes, drums on that car.
If you had everything stock, 9 inch drums, slant 6 engine, you still would have the small, 4 inch, small bolt pattern axle shafts, and wheels on that car, unless it was built as a DISC brake car.
What brakes are in front?
Disc, or Drum?
You have 4 1/2 inch bolt pattern wheels, on all 4 corners?
Or 4" in front 4 1/2" in the rear.
Lots get changed over, in 40+ year old cars.
