In a respect they are aircraft engines, but with a water jacket band across the upper fins. They left the head as air cooled but they did make "speed" versions, which is more of a heli motor the way it is timed, and run an ABC cylinder instead of a ringed piston with a water cooled head button and jacket. This allows the water jacket band to be left off and a full wall of cooling fins to complete the job. If you study Webra engines, their marine verisons (RCW's) use a differently timed sleeve and piston than their aero counterparts which tunes them to boating characteristics.
Here is one of Webra's later offerings for the example, it is my restored Speed .40 with Dynamix carb. Still an alky burner and completely a marine design. Most have fallen into the idea if it isn't a rear-intake drum induction engine, they don't qualify as a marine engine for some reason, and I can never help myself to dispute that!
It's my pride for Webra's that do it...lol.
If you look at the head button and compare it to a nitro head, you will see a major difference in band width area before the combustion dome.
Webra's are a little bit of a different animal than what people are used to seeing in model engines, but once you understand them and what they require, you'll be more than happy with them.
What Lewis will see if he pulled the head off of his is a baffled piston, and a recessed head to accept the baffle thats on the piston. This is the early design of scavenging exhaust gasses, one step before "scnerule" ported sleeves. Glow plugs that include an idle bar across them is almost necessary with a baffle piston to keep the glow plug from drowning at idle.