A lot of people seem say it can't be done properly, but then again, they have never done it.
This thread seems to suggest it can be done with some slight bulkhead mods / holes for the heater.
I've just bought a '96 Turbo as a donor for my Mk3, and am going to do the dash swap too so I'll let you know how it gets on!
Having the full van in full working order should help a lot as I can swap the entire loom etc. if needed.