OK.
I won't be able to blame the PO anymore.
New transom wood had delaminated from the fiberglass.
Lifted the deck - I thought - and realized that I had lifted the whole damn thing off the trailer. Eventually, I started to hear a zipper sound & the hull dropped back into the trailer ... only it took the splash well with it. The splash well, where it wraps over the top of the transom had been glued with liquid nails AND riveted to the transom. Then, the top and bottom had been foamed together with "Great Stuff."
So, outta this deal, I'm getting a new floor (don't even ask about stringers, I'm afraid to look right now), new transom, new splash well ... might even make me a fiberglass "fastback" tonneau cover. To think I started out thinking I could ratchet my transom into place and build some bracing to tie it in to the floor. I'll spend tomorrow afternoon on the phone with Express Composites and get some material ordered. With some determination, I'll be water worthy come June. Maybe not pretty, but at least she'll have good bones. Wish me luck.