Hi Lucky. Start with a 13-6 and go up from there. The Sportster 65 is a serious lugger. Kinda like the big block of the 60 series. It spins a big, long prop at lower rpm's. A wood 14-5 or 6 would be within this motor's capabilities. Just check the rpm's. You want it to max out at 9200 or so rpm's. Anything over 10 grand is just abusing this engine. It is timed and ported to run around 9 grand max. I have one, it will spin a MAS black 13-6 all day effortlessly. With say a 14-4 or 5 this thing will make that UCD a ballistic missile. It will pull that thing verticaly like it has no plane behind it. And don't worry about weight. It is actually a very light engine for it's size. Go ahead and use it, you will love it.

Mark Shuman