ok to convert 10 x 1 3/4 drums to 11 x 2 1/2 on '72 dart?

So if I understand this correctly, when I put 11x2.5" inch brakes on the rear of my 68 B'cuda when I swap in the 8-3/4... Swapping to 11 inch backing plates and drums from my parts stash, will not simply work with my original sbp axles if I re-drill them for bbp? I have not looked at it closely yet since it is about a year away, but with that, I'm assuming the wheel mounting surface is out further for 11x 2.5" brakes, not just a deeper backing plate? If so, then I'll get the spare axles I have for the Fury cut/re-splined.