Kaos : I have a Mag 91 four stroke in my UCD 46. I use a 14 - 4W APC prop. I had fits with it inverted. I ended installing it at 90 deg. and have never looked back. Line up the center of the tank with the center of the needle valve as best you can. I had to cut away some of the wood where the tank goes and then add what ever was needed. By the way Tower has a sale on the 91 FS for $169.00 less $20.00 with Sale # ??? This makes it very attractive to me.