Hi, James 100 here.
Yeah, as Paul (moose) said, I did this 2 weeks ago, but the other way around.
As already said, engines are virtually identical. Even the engine mounts, so no need to swop them around!
There were only a couple of small differences (bear in mind I have a 1996 defender and engine came from a1996 disco):
1) disco engine had cruise control on pump, which my defender did not have, so you may have to swop pupmps for easiest route.
2) disco engine had sensor of some sort on top of head, which again defender did not have, so now unplugged. Not sure what it's for, but looks like a temp sensor of sorts.
3) Wiring looms are totally different - disco has battery under bonnet, defender has it under passenger seat, so basically, use your original disco wiring loom!
Possibly some hoses may be different, so use original ones.
Are you changing clutch/cambelt as it makes sense, seeing as you need to remove engine or gearbox anyway to do this! (well, clutch anyway)
Also I would use the oppurtunity to flush out the radiator and intercooler, seeing as they are coming out also!
Hope this helps!
James