What exactly are you getting at? How much the brakes add to the width of the axle compared to the bare housing? Or how much they add axle to axle?
This sticky shows the measurement of the bare axle housings and the measurements drum face to drum face. The "flange to flange" measurement is a bare housing measurement.
As for how much it adds, it depends. The SBP drums add a different amount than the BBP drums. For example, a SBP A-body 8 3/4 is 52 5/8" for just the housing, and 57 1/8" drum to drum. So the SBP drums add 4.5" to the width. But a 65-67 B-body 8 3/4 is 54 1/4" bare, and 59 1/2" drum to drum, so the BBP drums add 5.25".
Disks usually add about a 1/4" to the width, per side, compared to drums. Obviously it can change a little based on what kit you actually use, but that's the general idea.