After a lot of work pulling the engine forward far enough to get the thicker diff back in, I got the engine back in its place again. Filled tranny with new synthetic 75W90 Valvoline and reused the O-ring n the side cover (even though I still have a new one from the gasket set). If you turn one wheel, the other one turns in the same direction as it should with a LSD
It turns nice and smooth by hand.
Got the engine running again and went for a test drive.
No extra noises, all seems just fine and dandy. Did a deliberate lighting of the tires in second gear (cold and damp road) and that felt different somehow, more aggressive in a way, but not out of control.
Car is still stupid fast and seemingly effortless at doing so.
At home, tranny is still bone dry as before.
All in all, this was relatively easy sailing, though I didn't know that up front..
Gotta love orginal parts