Ooohh, I really like John Faul's version. Of course, being a longtime Mercedes-Benz enthusiast perhaps I'm a bit biased....
Whether or not the subject is an air racer, the idea of a Merlin or Griffon P-38 has always intrigued me. Why a Merlin wasn't tried during the war I don't know; it worked perfectly well in the Mustang. Perhaps it had something to do with various entities being vested in the Allison, or not enough production capacity at Packard to supply both the Mustang program and another that would require twice as many engines...that means a tripling of production or a reduction in the number of aircraft produced. Post-war, a Griffon with contra-props would be wild.
With respect to the F7F and moving the CG aft when using big iron like the R-4360, that sounds like an excuse for two kits and a mild fuselage stretch. A couple of Monogram 1/72 kits could probably be found pretty cheap, and I think that somebody makes the Corncob engines in resin. With two kits' worth of engine cowlings it ought to be straightforward. Hmmmm....