Mk1 Engine Transplant

Could anyone tell me how long a job this would be, and which bits from which cars to use, as I have a very slow mk1 diesel sat on my drive next to a rather rusty mk2 gti, so my brain has been a thinking and come up with the obvious solution!!

How good an idea would this be? Need the mk1 up and running by march ideally!! Also potentially could get hold of a 1.9 audi turbo diesel lump and loom, what sort of job would it be to put that in?

Cheers for any help!!

Tim