To reply my own question, I filled the bottom end of the diff to 16g (weight includes lower aluminum case assembly + metal shafts + aluminum joints, I forgot to weigh it dry).

All gears were lightly sanded to remove flashings from the ejector pins/molding on the flat side. Since the green gasket that comes with the aluminum diff cover is slightly thinner than the brown ones from the plastic version (0.4 vs 0.5), using 0.3mm shims on the top and bottom felt way too tight and notchy.

I ended up with 0.2mm (0.1+0.1mm) large bevel shim on the cover side, 0.3mm on the bottom end, and 0.1mm on small bevels (all shims from large diameter shim kit 42313 with orange TRF orings).

So far no leaks yet and feels smooth. Obviously, the above may vary from one assembly to another.