Wind, I have a RCV .90 going into the new Hangar Nine P-51. My experience so far is limited to breaking it in and then running it just for fun. It is not a tweaker like an OS, it seems to be a set it and forget it engine. If you take a good look at the pictures you'll notice they have proportionally much more cooling fin area than a standard four stroke, even the prop driver has sizable cooling fins.
I'll be using a four bladed 17x10 Zinger at about 4,200 rpm max.
Ed, this is something that may change my mind about using the RCVon the P-51 is if I don't feel the airflow is sufficient. You will be pleased and surprised at the smoothness of these engines.