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

cudamark said

if you're going with the 4 1/2" bolt pattern, make sure you get a set of brakes that match. If you decide to use the 10 X 2 1/2", get backing plates, shoes, hardware, wheel cylinders, and drums for that application. Same goes if you decide on the 11" brakes. They made different widths of brakes in both the 10" and 11". The individual parts need to match or things don't work right.

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OK things are a lot clearer now.
One other caveat, I've located a set of backing plates that are 11 inch. But here's the other sadly and uniquely Canadian thing. I found out this summer when swapping an 8 3/4 out of a 68 Dodge (unknown model) that it came with 11 x 2 inch shoes. Let me tell you they are ridiculously difficult to find.
So one more question is there a way to check that these backing plates I found are not for the 11 x 2 inch shoes?

Edit.
PS the 68 Dodge 8 3/4 went into my son's 56 Custom Royal