I dont race anything as big as Antique for the cost and no air field for it, but I have found most engines turn about the same rpm. I think the reason is because the spinner is moving that air to the prop and loading it a bit more not sure.

Do you plan on running the 400cc moki in it? that would sound great and it swings a 40" prop

an even better sounding engine is the 20cc 3 cylinder by Kolm engines not sure on prop size though.

The herby 280 redone by Starr turn a 32x10 at 8,500 but with extreme noise.