Difference in drum brakes A-B Body

What is the offset difference of small bolt pattern drums from an "A" body 8 3/4 to big bolt patter drums from a "B" body 8 3/4 rear axle?

From my understanding, "A" body SBP drums are 1 3/4" and the "B" body BBP drums are 2 1/2". So the difference is 3/4". Am I correct? And I assume that any "B or C" body drum brake will work just fine on my 8 3/4?

Sorry for such a dumb question, I know I'm over thinking this right now. The answer is simple.

-James