You can mount the engine anyway you like and by deflecting the muffler you can keep most of the engine snot off the plane but never get away from all of it. Just the nature of the beast.
I have the OS 91 on my 60 size Kaos and it's A very good engine. All of my OS four strokes have been great. I just had to replace the muffler on mine this week. Be warned, OS is very proud of there parts and it shows on there prices!!!!! [&:]