Without a doubt, one of the scarcest racing engines made by an otherwise major pleasure engine producer was the McCulloch line which eventually became the Chrysler and then finally became the Force line from Mercury Outboards. Featured in the picture is a 1950s - 3 Holer near 60 cubic inch 3 cylinder engine. It was a 3 carb crankshaft rotary valve deflector pistoned engine what produced some 90 horsepower. Used in APBA and NOA (USA) class F racing the engines were never plentiful and mainly competed with the Mercury Mark 75H engines in class F before Loop Charged engines started their increasing domination of Alky racing. These McCulloch engines shared some similarities with their reed valved three holer engines but had more power due to the crank rotary valve induction system being used. On the collectors side these engines are few and very pricey in the collectors market.

This racing picture is believed to be a class X version of the McCulloch 3 Holer racing engine. This is no way to drive a raceboat! Enjoy the picture.

I have read that these motors had a belt driven external intake valve. You state that this version has a crank rotor ... what is the difference and which is correct?

From the ones I looked at in the 1960s and they were not plentiful the rotary valve was part of the crankshaft that rotated in what looked like would have been a type of crankcase block that surrounded the crankshaft not that dissimilar to the Hot Rod crankshaft. The crankshaft itself has wedge type openings to fit the surrounding valve bodies. Unfortunately there is not much one can see from an assembled engine and back then being a newbie I did not know and could not recognize a whole lot. Hopefully some one else might get some info.