OK - replaced the transfer case - yeah!

It was not too bad a job, although a lot slower than I thought. Here are the steps I took, together with things I would do differently next time (there better not be a next time, with this truck anyway!):

1. Remove the cross member support - (8) 5/8" bolts. The case then drops down slightly which helps access. Remove the 2 studs from the bottom of the case at this time to avoid potential damage to the studs if things get out of hand - the new case doesn't come with the studs.
2. Disconnect the electrical connector and unclip a cable going into the transmission.
3. Disconnect front and rear driveshafts and completely remove the front driveshaft. First remove the (6mm) allen bolts securing the rubber couplings on both the front and rear driveshafts; now rotate the front shaft to get a wrench on the (4) 5/8" bolts holding the front driveshaft to the transfer case output shaft. It might be better to undo the driveshaft rubber couplings before removing the cross member as they then wouldn't be angled down so much. (This is all probably a lot easier with a proper lift; I had the front wheels on ramps and the rear on the driveway, so couldn't rotate the wheels, and hence the shafts, to gain access to the bolts).
3. Undo the 5/16" bolts holding the transfer case to the transmission. These are hard to access at the top, but doable (I just used a small ring spanner (wrench). I couldn't get a socket on them, even with a universal coupling.
4. Use a jack to help take the case down (and back into place), but (as others have stated!) you NEED a buddy to help you ease it into position while it's balanced on the jack, operate the jack and give words of advice as you decide whether to risk damage to the case or your left arm as the case slips off the jack.
5. Once the case is out, transfer the breather tube and fittings to the new case. I tried to disconnect this before removing the case and managed to break the plastic fitting that plugs into the case; duct tape is now holding things until I can get a new fitting.
6. When installing the new case, angle the rear of it upwards to clear the exhaust system and then level it out to mate with the transmission.
7. Use blue permatex threadlocker on all the bolts. I used it on the allen bolts as well, although there appeared to be a green substance originally on them - hope it's Ok.

It all seems fine now, no clicking. I may have to adjust the transmission linkage though, as sometimes it will not come cleanly out of Park. Maybe the removal of the cross member and the slight dropping of the transmission caused this? Not sure how to adjust it yet - need to comb the archives...

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Graham