no dont take the case apart or change anything about the exhaust port. Do a search on "25cc Stihl" in this forum and you'll find some pics. Ken Lambert, Lambertrc.com converted my Stihl for aircraft use. Ck out his website! Ck out his CNC machines! I dont know how busy he is now but he could machine a hub for your boat prop. I guess you will leave the recoil starter and rail mount this bad boy?[sm=surprised.gif]