If it helps, I believe the 6L80 is 18" tall. So adding maybe 6" to that for the transmission jack, you'll need about 24" of clearance to roll that thing out from underneath.The more I think about it, I am going to do a functional test of what I have. I will jack up my Escalade with:
-3 ton jack stands under the rear axle, as high as they will go
-6 ton jack stands somewhere under the front frame, as high as they will go, sitting on 2" thick wood spacers
I will raise my transmission jack as high as it will go, and see how it all is. See how much room I have, see how well the transmission jack gets to the transmission.
Then buy more stuff accordingly.