There is no guide I had heard off.
Just a few words to give you an overview.
We have generally two different types of used engines. The industrial Diesel engines an the ones taken from a donor car.
The mostly used former car engine is the Daihatsu. A watercooled triple with 998cc. Availible with and without turbocharger.
We have also builds with the 800cc engine form the smart and the 1200cc TDI triple used in the VW Lupo and Audi A2.
Some guys even decided to use bigger four cylinder engines. The smallest availible was used in the Citroen AX od Peugeot 106.
The biggest and heaviest car engine used (until now) is the 1600cc four cylinder used in a wide range of cars from Volkswagen.
On the other side we have the industrial Engines. "Original" manufacturers are Hatz, Ruggerini, Lombardini, Kubota, Yanmar and Farymann. These manufacturers have distributrors everywhere in the world. Some of us are buying the engine they want from the local distributor, other use the engine they found in a broken something. Just to see if it fits in a motorcycle. Building diesel motorcycles is anarchy
Because of the high price level of these engines we have a market of mostly cloned engines from china for some years now.
The brands Kama and Changfa are known for a clone of the popular Yanmar L100V engine. Punsun and Kipor brought us something new. A range of V2 diesel engines. Air cooled from Punsun and water cooled from Kipor.
At least there are some engines that could be used if there where availible. I've listed some of them on my site:
http://classic.dieselkrad.info/motoren.html
Conclusion: Very few new engines for ten years. The smart cdi was introduced in 2000. And it's still the only car engine with "motorcycle size". The next thing will be the Tata Nano in it's diesel version. But nobody knows when this will be offered to the public.
Hope this helps
