Torsen LSDs were optional on all 1.8 cars. You can often judge whether a car had one by looking at the installed options, color, etc. No A/T car had one. Here are some helpful options lists with which you can infer, for instance, that any '95 car painted Merlot Mica (sparkly purple) with a 5-speed also had an LSD:
The 3.9 was found only on 6-speed NBs.
From '90 through about mid '95 or so, the axles were two pieces. A short "stub" axle that plugged into the diff, and a loner section containing the CV joints and the part that went into the hub.
Here's an early 2-piece axle, without the stub shaft attached:
And here's the stub shaft:
Later cars used axles that didn't have the removable section on the end. Here's a pair of late-model 1 pieces axles:
From '94-'05, the axles are freely interchangeable, regardless of whether they're 1 piece or 2 piece. The exception is that the MSMs got a slightly different differential which used different axles. So you can't use MSM axles with a non-MSM diff, or vise-versa.