Model diesels are not really diesel engines, but rather compression detonation engines. Model diesel fuel runs aroud 30-45% ether. Compression ratios on 40 size diesels are about the same as 40-size glow engines. In fact a 40-size glow engine will run fine on diesel fuel once it warms up. I would think an ST 40 dieselized would swing an 12 x 6 prop better than 10,000 RPM.

Jim