You could snag the turbo diesel plumbing off of a MK2 TD - should be fairly straightforward to install - I've owned both MK1 diesels and a MK2 TD - the TD was a lot more fun to drive. You'd want to get the exhaust manifold, turbo, downpipe, airbox and plumbing to go from the compressor side of the turbo to the intake manifold - doubtless you'll need to do some fabrication - but it shouldn't be a daunting proposition.
A 5 speed will give you a bit more top end on the highway (especially when combined with a turbo) - I believe the diesels had different gearboxes than the gassers to accomodate the lower revs and additional torque of the diesels - but I've been wrong before!
