I did it the cheap way:
Go for an Audi 80 16v as they are more common/cheaper than Passats or Corrados
My 1991 16v Quattro was £67.00 off yeBay and i simply swapped the entire engine over.
Your stainless exhaust manifold (lucky sod!) will fit and the standard inlet manifold bolts straight on. The cooling sytem is identical too!
As for cams i took both out of my 1.8 16v and put them in the Audi (6a) engine. Apparently only one is different but best swap both to be sure
The only problem i have found is the head have different temperature sensors- look at the distributor end of your head and there are some leccy connectors around the cooling pipe- my Audi engine had these in different places and one works the choke, another the ecu so make sure you note what goes where (i didnt, have guessed and the choke isnt quite right yet!) Its not tricky, and the Haynes manual explains the wiring colours anyway! Obviously this doesnt matter if you swap heads over, so maybe this is the better route (and you can check the bores and fit a new head gasket for peace of mind)
As for price, look for a short MOT 16v Audi 80 or Passat estate as they are less likely to be ragged (all will be high mileage though, mines done 160k) and after all, no one wants ropey old cars around xmas! I reckon £150 should get you either a car or a handily-sized scrapyard engine.
