I fixed my hole different then that, I wish we were all doing pic's back then so I would have taken pic of the work. :'(
But what I did is left the outside skin alone, I went on the inside and squared off the hole, and added two 3/4 pieces of ply, and glassed it all in.
Then went to the out side and just glassed matt in layers till I built it out to the same level as the rest.
My crazy thought at the time is if there was any pull form the out side the plug I made was bigger on the inside and never fit out the hole it the transom.
But after a few years of watching and learning, I know now that was never going to happen.
Good work BS!!