We have a fiberglass shop here that is cutting the transom out from the outside, they say it's the only way to do it. I'm not sure how strong this would be. Your comments, I can post some pictures/web page if you want.
Gotta agree with Deep....Split the cap, replace transom wood or pour it, put cap back on....done. Why chop it up if you don't have to? Looks like a nice boat, what model Glastron is that?