Yeah Lofty, they sound cool, but unfortunately they have quite a few drawbacks.... one is that you cant stop the engine, then start it again without pumping the oil out of the lower cylinders and turning the engine backwards ..... then when they start it is usually a smoky affair. Also, because they only turn at 2300rpm max, they really need to swing a big prop, like 80" or more, which means a tall mast/high seat/climb in... on a pusher, so they are really a tractor engine.... I am not sure they could cool effectively in pusher, or if they are even approved as pusher engines?
But you are right, they do sound awesome
The pics are of Murray Barkers Little Wing with the 'Rotec' radial. Murray did an awesome job building this one