We started the task of replacing my busted rear crossmember on Saturday. 8 hours later we had the old one out, and the new one resting in place but not yet welded.
I bought a replacement crossmember from Tony at Rat-co. People may be familiar with his replacement TR6 frames but he can supply other bits too. He send me a new crossmember that is much stronger than the original as well as some reinforcing pieces and gussets. The C channel wraps around the frame at the location where the old crossmember was mounted and generally strengthens that area.
I did not have to remove the diff, just lower it to clear the front and rear studs. I did remove the rear section of exhaust to give us easier access. It is a stainless exhaust with band clamps so it comes apart easily.
My temporary repair to the broken crossmember had held up well despite the poor weld on the inner most fracture (could not get at it very well).