Funny, I've seen this boat several times now and was just looking at some pics from last Friday and noticed the original speaker holes. Mine is the same way, hidden behind the upholstery as mine was radio delete. I like the location of the ones you have better but I really don't want to cut into fiberglass.
After my new upholstery job, I don't even want to cut holes at all. Anyways, it allows for larger speakers down low and doesn't contrast with those side panels. I'll have to think about this. How much room is behind those speakers? Seems like they would have to be shallow depth.

Hope you don't mind me posting these pics but wanted to share thoughts.