I would say you are about right with the hp. numbers, the torque numbers might suprise you and creep up in the mid 60's. You spin that crank that hard and have the cam, ports right then that motor should hang in there pretty deep on the rpm band when the load hits it, so long as the carb. can supply fuel when the rpm's drop. That is the biggest thing when using bigger carbs. is finding one that will supply top end air, but also supply bottom end fuel. With that bore and stroke combo. you may end up R&Ding your own cam. most of the 60 ci. flat singles out there are either using a 3.75" or 3.875" stroke. They were 50 ci. engines that the bore went bad and eventually some clubs made a class for them, some open super stock flatties come from that situation. The commands will out spin you with their rpm band but you will out torque them, some of the command guys really don't load their motor they just crank it as hard as they can and limit the gears so they don't run out of power, drop a gear and spin it harder philosophy.