However I'm still not sure if the perfect aviation diesel engine already exists? Not sure about modified car engines. My choice would be nothing that needs battery power to keep going.
That narrows the field to anything with a mechanical injection pump. The Weslake Dieselair engine in its original form (as flown in a Luscombe Silvaire) and the French Gazaile which used the Peugeot/Citroen 1.4 from the 106/Saxo, both qualify.
http://gazaile2.free.fr/img/imgFini/moteur/diesel.jpg
https://translate.google.co.uk/trans...r/&prev=search
The downside of mechanical injection is reduced efficiency (compared to common rail diesels) and lower power to weight ratio.