Greg,
I suppose that technically speaking, you don't have to remove the rear flange nut. I took a while to answer this because I've never done that. In short, other than working on the electrical part of an O/D, my advice is that if you do anything to one, be prepared to do EVERYTHING to one. They are a bit complex and mysterious, though certainly not beyond comprehension. The parts can be fiddly, and hard to contain. That's why there are guys who specialize in just this area, like John Esposito at Quantum Mechanics.
When trying to keep it all together, work with the whole gearbox vertically positioned, bell housing down. If you've got a manual, live with it for a few days untill you feel you know what to expect. If not, by all means, get one. Good luck.
Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon