To try to find the current owners of similar boats got to Yacht World and do a search for Grand Banks 50's. take note of the boat names, then go to the NOAA documentation website http://www.st.nmfs.noaa.gov/st1/CoastGuard/index.html
and enter the names of the boats. If the boats are documented you will then have the owners names and addresses to contact them directly. If they are not documented send an email to the listing broker asking to forward your email to the owners to see if you can get copies of some of the documentation you are looking for.