Wow, someone is as crazy as I am!
I just bought ($500) the same exact boat a few months back and am doing a similar restoration. I have twin 305s/pre-alpha(?) outdrives in there now and am unsure if they are worth even trying to get to run, 1100hrs and used in salt water. I am seriously considering converting it into a single engine to save on fuel. Plus I have a good newer 350/Alpha 1 donor out of a ski boat that will fit nicely.
As far as the core samples, I'm not sure exactly where you took them, but the shower is on the right side, and I found no foam under it. Also I had water there too, I took the shower drain apart, and lifted the little black cup that the pump sits out. It was only held in by silicone, just don't over do it and break it. I then pumped all the water I could out through the hole.
My center floor what shot from where you step into the cabin back to the engine compartment. Its a simple fix, just pull up the carpet carefully and put a new 3/4" piece down.
If you get a chance, can you take a picture of your cockpit (back deck) with the engine covers in place. A previous owner just put plywood over it and it looks awful. I want to make new covers similar to what your smaller hatch looks like.
I have ripped most of my boat apart, so if you have any questions that I may be able to help with, let me know. Also, check your bow rail fittings, they seem to be a flaw of this boat, they may look awful, but worse mine would not hold up to even a good shake. I just wouldn't want you to lean on one and take a fall down to the hard ground.
One more question, does your boat have a black water tank? or just a porta-potti? I want to add a black water tank so that I can spend 10+ days on the boat without needing a pump-out. I was thinking of putting it under floor where the helm is, but I'm not sure what is under there, I used a hole saw to take a look, but its filled with foam. I'm not sure if there are any cross braces, etc. that would get in the way.
Good luck,
Greg
PS. Nice shop! I wish I could fit this into our garage, its cold up here in upstate NY!
