8 3/4 backing plates onto a small bolt with upgraded big bolt shafts

The '65-71 1/2 ton Dodge PU's used the 11 X 2" brakes as well as a few low end '65-75 C-bodies. Unless you have other known backing plates to compare them with, the only way will probably be to take them to the auto parts store and trial fit shoes against them to see where they hit the top pin and if they line up straight with the wheel cylinder push rods.