7 1/4 10" Backing Plates

I can verify that the LBP 7.25 I took out of a '76 Dart 6cyl 4dr w/discs has the 5th stud at the bottom, which makes sense, same backing plate as every other Mopar with 10×2.5" shoes.
*EDIT* I will add that the '73 360 Duster 8.25 rear I have has 5-hole backing plates, but only has 4 studs/holes in the housing flanges.