First I have a picture of the underside of the deck. The top of the picture is forward, the bottom is aft. If you think about it like you are laying on your back it might make sense.
Here we see the support structure for the sampson posts. There are two lateral beams glassed in forward and aft of the posts. A section of the fiberglass has been cut out to show the wood of the posts. The wood looks shiny because it's wet. This is one of the main problems with this design. Since the interior is entirely encased in fiberglass, any water that enters through the joint between the sampson post and the deck stays inside the fiberglass case.
The base of the sampson post has a lateral bolt that holds it to an interior spacer block (that's the middle part of the black section in the previous picture). This is a close-up of the end of the bolt showing how rusty it is. In addition to the lateral bolt, there are two fore and aft bolts that hold the sampson post to the lateral beams.
This is a close-up of one of the fore-and-aft bolts after the sampson post has been removed. It's probably stainless, but in the environment inside the fiberglass casing it rusted like mild steel.
Here is progress to date. The sampson posts and all the teak deck have been removed. The deck is solid, so from here I'll inject some penetrating epoxy and then fill in all the screw holes before sanding it clean and smooth. The holes for the old sampson post will be fiberglassed over and this stainless version will be fabricated.
One funny thing about this project, with all the anchor chain, anchors, rodes, bowsprit and pulpit removed, the waterline is up about 7 inches forward (click the image for better resolution...). I borrowed a bathroom scale to weigh some of the parts that have been removed. The sampson post and some of its supports weigh almost 40 lbs. The bowsprit, just the spar not including the pulpit, weighs 140 lbs!
Here's a little composition to show the other major problem with the existing setup. A lot of the fiberglass case is delaminating from the underside of the deck. I've done a little bit of prying to get the edge open, but it was very easy to insert the head of the pry bar under the fiberglass. All this loose glass will be removed and a new support structure will be added.