I oredered my engine and plane and the hardware kit from Tom at WH. The engine arrived with 3" standoffs and I still had to shim the engine about 1/4". I have the pitts style muffler that also came from Tom so I can't help you on the different muffler types. I did have to cut some of the cowl th make room for part of the muffler but it doesn't look bad at least in my eyes. Bill