Scott,

There's a company that makes specialized exhaust systems, I believe there name is Kleo Creations or something like that? I saw a picture somewhere of a custom exhaust stack for (I think) a P-40. Might be worth some searching. You could probably get away with something made out of tubing with the RCV being a 4-stroke. Of course, then all that ouly exhaust will be running down the side of your fuse instead of out the bottom of the cowl!

Bob