The ARL motor is used as the high performance Diesel engine in Germany and other parts of Europe.
It's a really good base for tuning and overall reliability. You have to use the VW ECU. There's no other way around it. This engine is too complicated for any stand alone systems since they turbo is vacuum controlled with variable vane technology rather then a waste gate on the turbo. It has pumpe duese injectors which are also controlled by the ECU in terms of timing and injection quantity.
A Diesel engine is a very different technology to work with. There is no butterfly to control rpm and power. This is completely done by the amount of Diesel injection. We don't have a situation where your engine can run lean. If it smokes you add air, if you have a lot of air and it doesn't slightly smoke under WOT, you add fuel. That's it. Nothing else matters, as long as your timing is correctly set.
Check out www.tdiclub.com and look for the performance section. You'll find enough info about the engines etc. It's a very good forum.