As it happens, I have just installed my rear drive train.
I am using standard drum brakes, 7" diff & push in shafts.
Tis very difficult to measure with any degree of huge accuracy but for what it is worth, here is the best I can measure.
From drum outer face to drum outer face, I get something in the region of 1530mm ( 1529mm to be exact )
As said, it is an approximate measurement due the back of the build being on stands & the hubs are not set dead upright ( took a mean average measurement though )
I believe the measurement to be accurate enough to give you some idea if you are in the same ball park