I did the same job on another car recently with a similarly heavy box (Triumph 2000). It's not too difficult with the right equipment, and an understanding of what you are doing.
You need good ramps or really solid stands for the front of the car. Then support the box, remove the cross member, disconnect the drive shaft, shifter lever, etc, and lower the whole assembly until it drops enough for the clutch housing to clear the firewall. Then put blocks under the sump pan to take the weight of the engine. Put a trolley jack under the gearbox, just take its weight, and release all the bolts and the starter. Slide the box back to disengage the input shaft from the clutch, lower the jack, and slide it back so that you can get at the clutch.
Points to watch:
1) NEVER let the box hang by the input shaft. It will damage the clutch plate, or the shaft, or the gearbox oil seal, or the extension housing
2) Replace the release bearing, not just the clutch
3) take the opportunity of replacing the gearbox front oil seal if it is leaking.
4) Use or make out of a bit of wooden dowel a tool for aligning the clutch plate on reassembly.

It depends on how much experience you've had and how important it is to save about $300. I think you need a good (not the little cheap ones) strong stable floor jack, beefy jackstands, a nice smooth paved surface, the right tools, patience, and at least one strong friend. My son did his clutch recently on his M46 with the help of two friends. All three have experience with tools, etc. They got it done in one evening and the next day. It's a greasy grimy heavy job. I was glad I was just observing this one. I would do my own though, if it needed it. I have the luxury of a garage and an extra car so I can go slowly, wait for help when I need it, and plan it out carefully, etc. It can be very satifying every time you shift after you do the job, plus you'll really understand the workings of the clutch, etc. I'm not trying to discourage you. Just realize bdfore you start that it's not a walk in the park. Good luck.
--
Thanks everyone for all the help, Doug C. 81 242 Brick Off Blocks, turbo bars and wheels, M46; 86 244, B230, 150k , auto.

Mechanically inclined, have suitable tools, space, time, temperment, and "ALL" parst are at the ready ? Then go for it. Great feeling when finished (pro), despite all the grease under fingernails, and busted knuckles (con).

No need to worry about OD (that's in tranny repair dept.).

I've done a few transmission swaps in the driveway, and the most difficult part of it, other than the top bellhousing bolts and the grub screw locking the shifter pin into the fork, is manhandling the beast out without crushing your ribs or worse. It's NOT a DIY job unless you've got a hoist (ideal), ramps (adequate) or four very secure jackstands on solid ground. By necessity I did one laying in the mud with a hydraulic jack & a stack of 2x6s as support. It's not worth it. Trust me. You need height, and 2 sets of hands in there to do it safely. As far as the added complication posed by the OD, I've not encountered any problems during removal/reassembly because of having an overdrive transmission (transmission's a little longer, heavier, an extra wire to unhook, that's about it). Perhaps those posts referred to replacing the OD clutch itself? Not sure... But if you've got an assistant, and a decent place to work on it, go for it.
--
Chris, Dartmouth NS Canada 70 M-B 280SE, 83 245DL, 84 244 turbo, 90 780 turbo, 92 VW Golf