Mike Dec fly RC has a test and write up on the OS46 LA with a Davis head ( yes 46 not 40) the results in running maybe not in this plane but a very good insight and set up would be similar of course with a smaller prop maybe by an inch, both of these engines really come alive as diesel conversons with Davis heads martin

these engines are popular, durable, available,, not expensive, run on normal model diesel fuel just excellent 40 class conversion with no issues
martin