How to fill in I/O holes

[laser]

My transom looks in good shape so I'm not going to replace it at this time. The I/O holes seem good around the opening but there is some collapse around a bolt hole in each opening.
The openings are odd shaped so do I cut plywood to that shape or square up the hole. I assume that the bolt hole has to go to cut out soft stuff.
Does the wood get epoxy'd, glued into place then glass layered on both sides? I'm going to go with a bracket so I don't know how well the outside needs to be finished.

Bill

I support the 2 seacraft theory while one is a project