Couple things here.... what exactly are you planning to use it for? Because I would consider ANY T3 to be more of a hobby/fun vehicle, and to that end, I'd not be super concerned about how fast it can go, especially one of the heavier AWD versions, which I have owned. And even with the 95hp 2.1L waterboxer, the only choice we had here, it was no rocket ship... and it was just a regular 7-passenger van. I can only imagine that the same box with the 65hp JX would be only marginally better than the 48hp NA 1.6L, which I also own.
This is why engine swaps are so common.
The AAZ is not, nor ever was, a TDI. TDI = Turbo Direct Injection. The AAZ is not a direct injected engine. It is a prechamber diesel, like the 1.6L engines. It has a turbo, but no intercooler, and is probably only giving the engine about 10hp more than it would have without a turbo, had VAG sold such an engine.
The main draw the AAZ has is that just like the factory diesels used in the T3s, it is all mechanical, no electronics of any kind (technically the AAZ does have altitude compensation, like the very late 1.6L engines in the A2 Jettas sold here, but it is not a processor driven device, just an altitude aneroid that modifies injection timing slightly).
An M-TDI is a TDI engine, in this case we'd be talking about an early one like a 1Z or AHU, that has been converted (pump change) to be mechanical only. It is still direct injected, still uses the same injectors, same lower pump body, but the top of the pump has been changed to the old fashioned type that attaches to the cable just like the prechamber diesels. But again, part of the TDI's power, which is only 15hp more than the AAZ, is the fact that it can run a more aggressive boost and fueling map because it has superior combustion characteristics and an intercooler. A direct injected diesel is MUCH better at turning fuel into motive power, whereas prechamber diesels tend to waste much of that energy as heat in the cylinder head.
I have been around T3s (Vanagons) since they've been around just about, and I see and follow a lot of these non-passenger or camper versions that have been imported and one rule always holds true: you get what you pay for. Which is why I go back to the original question of what you are wanting to use it for. If it was 1990 and you lived in Sweden, then a syncro turbodiesel doka would be a great purchase to use on your property, run into town, etc. But in 2018, in the US of A, those same tasks would likely be better suited to a five year old F150.
People can spend obscene amounts of money on Vanagons.... I am a member of several groups, and it is quite nuts. I've seen some TDI converted syncro Westy vans with some other upgrades sell for $45k. You can go down to your Mercedes-Benz dealer and buy a 4WD Sprinter, brand spanking new, for not much more than that.
You are right in that a lot of the Euro imported ones, especially the trucks, are just quick and dirty reconditioning and maybe a fresh coat of paint. But looking underneath them you'll see they were used for what they were intended to be used for.... often for 20 years... then sat somewhere for five more, before being "discovered" and thrown in a cargo container and shipped here.
There are certainly some really nice ones out there, though. If I had kept all the Vanagons I have ever owned, I'd be sitting on a giant fortune right now.
