Radar, you will be fine with that engine. I had a 72 Saito on my Hog and had plenty of power. I guess it's because I'm older, don't know. Everyone else needs at least a 91. You can always convert to a 4 stroke later if your mount will work. I just converted a Super Sportster 60 to a 4 stroke. Or if you ever build another you can go 4 stroke. This is my second that I'm starting. Good luck.