This isn't a terrible job to do yourself - it's just no fun. In a nutshell... take the seat box/floor/tunnel out, disconnect the rear prop, and you should be able to pull the transmission out. I think I had my tub off at the time, but I don't think that was necessary. After that, you can get to the rear seal by removing the drain pan. The seal (~ $15) is sort of an interesting split design. Replace the clutch before you bolt the transmission back on.
I can't say doing it made me a better person, but it really wasn't that bad.
1967 IIA 109 Regular RHD
1993 Range Rover LWB (gone, thankfully)
1969 IIA 88 Bugeye (gone, unfortunately)