We replaced the head on Glory Days #115 last year with a Blake & Lavac head from Defender Marine. The technology by which the the pump evacuates the head is different than other marine heads - there is a seal in the seat, and pumping creates a vacuum that evacuates what's in the head. There was a Blake & Lavac on my husband's former boat (a 47' PJ) that served a crew of 12 on many Mackinac races. It is enormously reliable and easy to use. The instructions that you give anyone are: close the lid; pump 10 times; wait 5 seconds; pump 5 times. End. Nothing else to do.
Cost is only about 5-10% more than the conventional heads with the pump systems that only your regular crew can remember how to use.
I replaced my head this spring. My old head was held down with hex head lag wood screws. Similar to the the ones used to hold the mast step base to the stringers. My new head had a different hole pattern so I filled the old ones with epoxy and re-drilled for the new head. After drilling through the fiber glass I hit wood, so it appears that there is wood under the area where the head mounts. That's my final answer and I'm sticking to it. Good luck.
Has anybody ever replaced their head? I'm thinking about it but noticed the bolts that hold it to the floor seem to have the nuts(?) under the floor. There appears to be no access. I'm reluctant to loosen and hear the clunk of the nut falling off never to be mated again. Lance