Neil, A C90 will also work fine. They actually can put out more power than an O-200. Their rated HP was at 2500 and the O-200 at 2800 RPM. That said, the either can produse much more power with compression and cam changes. They weigh less and most of the parts are less expensive. The O-235 has unequal length intake tubes, solid tappets and those are not something that are positives.