Hi Joe,
I'm in almost the same situation as you - I have a 1994 Audi coupe with a petrol engine which I am looking to remove in favour of a 1.9 Tdi. My original thoughts were to purchase a 1.9 Tdi Audi 80 Saloon and simply swap the engines although I have seen others using the VAG 1.9 from Seats:
Audi Coupe Quattro TDi - Nowy Dwor Gdanski, PL
I'm still not 100% sure which option to go for - Have you had any more luck with your search?
Cheers,
Laurence