Haynes don't do one for the TD engine at all . I bought the haynes petrol version which gives you all the information on running gear etc. and also bought the just kampers kamper manual that covers the engine , gearbox and a few other bits and bobs between the two I have managed so far. Also alot of good info on the club 80-90 web site has come in very useful
I done the same as mrdp, haynes manual is very handy but works best in partnership with the JK manual. But exactly as stated I wouldnt have got anywhere without the help of the 80-90 members and the wiki pages. Also got a copy of the keeping your vw alive for idiots from a friend, good read and interesting but steered towards Aircooled, worth a look though.