The Doner..

There are quite a few suitable TDI engines for this conversion. Fitted to various models... Golf, Passat, Sharan, etc... mid to late 90's. They all had them. And then theres the other VAG models... plenty of Audi and Seat models got them too...
The most suitable ones are those fitted to the transverse engined cars. This is because the engine mountings on the cars with "Inline" mounted engines (all the Audis and Passats for example) are different to the Transversely mounted engines. Using a transverse engine means you can use the original T3 engine mountings, with the inline engines you need to modify or use custom made mounts.

Out of the the Transverse engines the common ones are the 1Z which is rated at 90hp output. Common on Golfs, and Sharans etc. And the AFN... The AFN was fitted to the Golf but we didnt see many of them in the UK. So, that leaves us with the Sharan (and Alhambra, and Galaxy for that matter).

The things with the Shalambralaxy is that they are generally big milers. Nobody buys a 7 seater to trundle to the shops once a week, they buy them to cart people and stuff around. Lots. And of course the Diesels are the most economical at this... so Diesel mileages tend to be high. So one with sensible miles and at the right price isnt necessarily easy to find.

Another plus point for a Shalambralaxy is that that its a big heavy motor. This means that when I pull what I need out of it I'll get a big chunk back from the scrap man for whats left :)

Eventually, what appeared to be the right car popped up on Ebay. 1999 VW Sharan 110hp with a little Road Tax and MOT and sensible miles. Tax and MOT was desirable because it means I get to drive it around legally for a few hundred miles to be confident there are no issues with the engine. Knowing there are no fault codes on the ECU relating to the engine is pretty importantant, and will make fault finding any that appear after the conversion easier.
Mileage on the car is 114000 which is low for a TDI. The car is perfect as its pretty rough around the edges, has short MOT and a load of advisories on the last MOT, and is generally in "banger" territory. Which means sub £500 price tag.
Despite this, it seems like a good car. Its been looked after for some of its life at least... Mileage checks out on the MOT database and it has nice good quality MANN fuel and oil filters, not the cheap nasty crap.
No service history or evidence of cam belt change either which for my purposes is another plus... the belts will be done anyway and the service history would just make it a more expensive car.

Needless to say, I bought it. Ive driven a couple of hundred miles and it goes well, makes all the right noises and generally drives as it should. All the bits I need seem in fine fettle.