My first response
is don't do it. The lines on a Hunter give it style and beauty. John Cherubini said, "A yacht should be graceful enough to be worthy of the sea." A Hunter Cherubini, in particular, is a masterpiece in design and its visual appeal is unmatched. There is poetic symetry in the rise of the bow to the sweep of the deck and fall of the transom. You want to mess this up by hanging an outboard motor on it? I'd rather you draw a mustache on the Mona Lisa. Call Sandy Hook Yacht and work with them to repair or repower the old inboard. Nonetheless, if you must, hang at least a 15 hp four-stroke on it. It's still going to cost you plenty. Best of luck.