I'm not sure if I'm completely following what your question is, but once everything is disconnected (i.e.- bell bolts, rear mount) the trans will have to move straight away from the engine a couple of inches to allow the trans input shaft to clear the pilot bearing and clutch. Then it can be lowered clear from the truck.
On all of ones I've done, what worked best for me was to have the jack* in place under the trans, remove the rear mount and cross member second-to-last, slightly lower the jack, then lastly remove the bell housing bolts and then roll the jack back to pull the trans away from the motor.
The problems I see if you don't lower the trans, and thus the back of the engine (at least a little), is that the trans bellhousing will likely run into the firewall / tunnel sheet metal not allowing the trans input to clear the clutch. And, the lowering also allows the shifter stub to clear the floor, letting the trans move to the rear.
I've never tried to remove an RBV trans without removing the cross member, or not lowering the rear. Others may have, though, and can give better advice to your question.
* I use a floor jack with a homemade adapter, just like you're doing:
(but yours looks a hell of lot better than mine, BTW!).
What really helps is to match the angle of the transmission so that it removes and installs
as straight as possible to the engine. My "Bubba adapter" is a clam-shell design with a hinge (seen on the rear), and I tap in a plastic wedge on the front to get the angle just right. You can use wood scrap on yours to accomplish the same thing: cradling the mission and matching the angle. I've used the rig in the pic to R&R transmissions behind a 2.3, 2.8, 2.9 and 4.0, autos and manuals. Not pretty, but it has worked fine for me for years.
Keep us posted on your progress. Good luck!