Transom rebuild Seaway 23'

Does anyone have input regarding a transom rebuild, glass over ply, upgrading to a 225 HP outboard. (485 lbs). Many Seaways have been built on the West Coast however mostly in boards this one from the late 70s, early 80s. I am wondering if I should keep the existing glass work, and just exhume the old rotted plywood from the inside if possible. And that will act as a surface to work off of. I have some nice three-quarter inch marine plywood, double thickness, and thinking about some oak beams to span across for extra reinforcement. where the Jack Plate will be. And considering some large angles ( knees) to tie in to the sides of the hull and bottom, any advice? Here are some additional images after an exploratory cut. The Blue tape will be the new transom height .