Ah, for myself, the last t-box/engine split i did, I used a small floor jack with a chunk of 8 inch board on it under the oil pan to take some of the load and support the assembly once you have pulled the crossmember and while you go diving for the various bolts. The trick with the large width board is that you want it to be wide enough that the motor weight isn't on the bottom of the pan, it is on the pan walls. That way the pan bottom doesn't get dished in or dented.
To grab that t-mission from below, unless you have a lift, you are going to need sufficient room to get the floor jack in and then get it plus the t-mission out. With a floor jack set up with a t-mission adapter plate, that works out to around 20+ inches. Most normal hard stands will not get you that high without having them sit on some kind of wooden beam. For what I wanted, i borrowed an idea from another thread here on the board and built a group of frames from 2 x4 laid flat that I could stack one on top of another to get my height. This is a static lift but it is stable and holds a load quite well. There are pictures of them in use, located on the Non G-Body forum hereabouts; not sure of the page number, it was back in the early spring of this year.
After that it is all mechanical. The only complication is that, if you want to leave the starter in place, you might have to drop the oil filter to get some room to access the converter to ring gear mounting bolts. The t-mission to engine block case bolts will be a PITA but can be had using extensions and a swivel or two. One thought would be to make a list of everything you have disconnected or unbolted so you can review what has been done to ensure nothing was missed. Other thing is to bag and tag the fasteners. Even if you decide to go ARP or whatever, the old fasteners make good samples for getting the right replacements the first time. If ARP, use their spec for torque. You can go the old "two grunts and a groan" method but a torque wrench, if possible, is easier and offers greater peace of mind.
Nick