I was thinking of cutting an inspection hatch in the side of one of the hulls to see what needs doing, or seperating the top half of the hull from the bottom around the seam. Has anyone else done this and do you have any advice?
Really there's nothing to be done about it. It's part of the boat. Ususally the flotation blocks settle in to a position and stay there. Turning the boat upside down shook it loose.
Don't cut a port in the hull. If you want to install an inspection port, put it in between the pylons on the deck. Don't put it on the foredeck.
This picture shows the location of the foam block and while trying to separate the boat at the hull/deck seam is a really, really bad idea. It isn't a piece of tupperware.