I mounted a 1972 40hp Evinrude on the back of a 1972 Pearson 36' sailboat. WE custom made the bracket and made a backing plate on the inside of the transom. Its held up for a year now with no issues(other then the motor giving up on life). If you make a backer for the mounting plate, it should be ok, just keep an eye on where the transom meets the hull sides.
On the otherhand, does anyone think a longshaft 15hp outboard would be enough power to keep the pearson going? The 40 is needed for another boat and ive found an extra longshaft 15hp Johnson to use. Ive moved the boat before with a shortshaft 15hp motor and had alot of cavation issues. I figure its enough power as long as the prop stays in the water. 15hp isnt far off what the little diesel was.