Currently doing one.
hardest part is getting all the little BS parts rounded up. :icon_bigg
Thank goodness the mkIII's have a place for the clutch pedal to bolt up to, unlike the mkII's. You'll also have to jump the neutral safety switch on the Auto harness to be able to start the car. I got a diagram somewhere that tells you what to jump. If you end up doing the swap and want some advice feel free to PM me.
My first piece of advice...
Pull the engine/trans at the same time. IMHO it's a lot easier and you have a great chance to fix oil leaks, replaces seals, do a timing belt change, clean the engine bay, pretty much do anything that would be a PITA w/ the engine in the car. If you don't have to do any of that stuff, it's your call. But by pulling the engine harness through the firewall, pulling an engine is like a 2 hour job by yourself.
Having to fight lining up the trans, torqueconverter/clutch/ w/e is completely worth it to me. But I'm not lazy, I just like doing it the easy way. Again, it's not the proven easiest way, but I've had a ton of luck w/ it.