AAZ is the engine type.
For example, the standard 1.9/2.1 water cooled petrol (WBX for short)
Engine Code Size in CC BHP
DF 1900 60
DG 1900 77
DH 1900 82
GW 1900 90
SP 1900 73
DJ 2100 112
MV 2100 95
SR 2100 87
SS 2100 93
As for the AAZ engine, AAZ's are not tdi's and as such, aaz engined cars would normally be badged TD.
Golf CL's and GL's mainly, but GL's switched to tdi's a lot earlier. Same goes for Passats. As a contradiction to that there are a few Golfs and Passat circa 94 that are badged tdi, BUt still have an AAZ and are infact TD's.
Seat Cordoba also, but I think these are very rare.
Generally speaking AAZ TD's came in in 92 and phased our around 95.
Further reading be;
THREAD - Fitting aaz into my 1.6td
THREAD - 1.6 to Passat 1.6td - I suspect this is AAZ conversion but I am not a derv man TBH.
THREAD - Diesel alternative engines....introduction
WIKI - Alternitave engines
JK THREAD - 1.9 turbo diesel in t25
As for place near you that will fit a high top, I am sure there is a place in Chesterfield who specialise in VW campers, and there is a place in Loscoe who work on campers (not sure if they just do camper conversions though)have a search on here/google or ask in gen chat.
Hope that makes some sense to you and is of some help.