Now that I'm done coughing fiberglass out of my lungs and picking it out of my eyes here's the update. The Navy taught me to write in BLUF style - bottom line up front.
No corrosion found anywhere. If I had not cut the chainplate into pieces to remove it I would have no problem putting it back in and using it for another 30 years.
Lots of silliness certainly. No part of the chain plate actually touched the hull proper - just the three or four layers of glass and resin that where draped over it.
In the photo's below you will see a short (3 inches per side) piece of round stock welded to the top. That was wrapped in glass and hidden right up against the overlap of the deck/hull - i.e. sneaky little last bit of 'what the heck is holding the damn thing in'.
All told - 6 hours to get the plate out - but a lot of that was expirimenting with different tools and methods. I bet I can get the next one out in 3 hours, if I bother.
all out - daylight coming in from above
Looking up - note the depth of the pocket the plate was in - and zero contact plate to hull.
Cleaned up a bit, and my chopper chisel laid in for scale
The beast. Chopping it up in manageable pieces seemed the best way to get it out.
Note the round bastard bar at the top.
Someday I will learn to focus a camera. There is no rust, no corrosion, no cracking.