What year? '96 models got a sealed output so you won't have leakage issues when you tilt it. Earlier ones will need you to seal up the output or you'll drain the ATF unexpectedly.
Unless you have a tranny jack adapter on that 3-ton jack, it might be a better idea to just press the t-case out by hand. Get an assistant to help if needed; I believe the wet weight of the NP231 was something like 65 (or 85?) pounds. It's not unmanageable, but it's not something you want to balance on top of a jack, either.
Sounds like you've got the rest of it figured out already. Good luck.
Jim
www.yuccaman.com