7.25 Brake Backing Plate Interchange

I've got a 7.25 rear end with 9 inch drums I would like find some 1O inch backing plates. My understanding is only the 7.25 has 4 mounting holes, all others have 5. Meaning that the only source is from a 7.25 with 10 inch brakes.
Am I correct so far?
I know that the ten inch brakes appeared on 7.25 rears in 1965. The 7.25 has never gone out of production as far as I know. I'm thinking of the Dakota and some Jeeps. Did they retain the 4 bolt mount?
What vehicles can provide a 10 inch backing plate with the 4 bolt mount usable on my early 7.25?