i converted my combi to tdi power a couple years back
its an easy enough job , from memory you need to cut and shut the downpipe and swap the engine mounts and flywheel then just a few other bits and bobs as you go , the wiring on the fuel advance took a bit of working out as did the immobilised pump !
the best engine to use is a TDi escort engine not the TD as the tdi has a bigger turbo / pump and intercooler it b
bolts upto the mk4 gearbox too
if you go for it i will have a look at how i got it wired so it runs smooth when cold etc
with the pump wound out you can get around 110-120 bhp (90 standard but it gets a bit smokey , best to just tweak the pump and you will have around 100 bhp and plenty of torque ,mine will piss all over my XR3i and keeps up with a standard RS turbo , upto 80 mph anyway then the gearing is too low , also get 35 MPG when driving like a loon and 50 MPG when i behave !
few pics of it: