Montague - i had the WM Ultimate with a 32SX and a bisson pitts muffler. worked like a charm. the pitts muffler just fit the cowl so the runner side of the muffler would actually hit the cowling. but it worked well anyway and i had some very nice flights on it. I not only had weight on the engine mount, I had the 4AAA rx battery ON the firewall with the electronic lead going through it. that was the only way I could get the desired CG. wish i still had it now (sold it when i moved)