This gentleman is apparently trying to bring a conversion kit to market using the Duramax industrial v twins:
https://www.facebook.com/share/1gnQ6fh8navFK72X/?mibextid=79PoIiHis ad states:
Kit with cdi, exhaust, and prop hub for Duromax 713 or 999 generator engines.
The Duromax 713 sells for $999 at many sources. It weighs 103.6 lbs, I remove 26 lbs of flywheel, starter, fan, etc. I add about 5 lbs with the conversion kit for resulting 82.6 lbs.
The original power is advertised 31.72 ft-lbs (43 N.m.)@ 2500RPM, max rpm 4000.
Prop rpm should normally be around 2200 so a great place for max torque.
I will measure the static prop thrust and compare with a Rotax 377 soon.
I plan to offer a light weight turbocharger kit soon.
I know nothing further about it but it looks like it has potential.