Since you mention a cowl, I'm assuming you want to hack the front end of the 4*, and put a non-stock cowl on there.

Pitts-style mufflers are designed for side or inverted mounted engines, and they don't go back behind the engine, meaning that they won't hit the firewall or anything.

Check out http://www.slimlineproducts.com/onli...mline_home.htm for a wide range of options. Slimline isn't the only game in town, but they have a good selection, and probibly have something to fit your engine.