ORIGINAL: Campgems
Sllimline make a couple styles, One for an inverted engine and one for an engine on it's side. The one on it's side is what I have on my Mag 91, but I havn't run it yet. I required a big hole in the cowl to fit as the end of the can is out there a bit, not as far as the rocker cover, but about to the base of the rocker cover. If you have the same Rv 4 that one of our guys have though, it should fit without much problem. If your engine now fits in the cowl, and you have clear space below the header pipe, it should fit fine. I'll send you a photo of mine, I don't have the cowl on right now. By the way, mine is on a Super Aeromaster that has a big radial cowl, but it is smaller than the RV 4 at the field.
Don
I installed the muffler and tried to install the cowling with little success. I had to make major mods to the cowl and when it is all side and done not worth it. Had to remove way to much cowling. I'm going to order a new cowl and go back to the old way.