My notes are not in front of me, but as far as aftermarket 60's go, the Strange unit that I ordered through Dr Diff was 2 lbs lighter than the Moser housing of the same size.

The factory units may be either heavier or lighter. If lighter, I would suspect that there aren't as many reinforcement welds on the axle tubes and or gussets like the new units have. Weld beads can add up the weight quite fast fellas. but I could be wrong.