I think your best bet would be to contact Catalina directly for the structural information - you'll get the best info that way (have your HIN number ready) By all accounts they are very helpful.
Beyond that I think you'll at least be doing some exploratory grinding sometime soon!
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"