Cal28 Chainplate material?

Hi All, Working on our flat top, hull 181. Portside bulkhead had rot as a result of a failed port. None of the damage was in proximity to the chainplate. I have soaked it with penetrating epoxy, made sister boards and filled the voids with coloidal epoxy. While working on it a friend made the comment that the chainplates appeared to be Monel. Anyone one have any info about the material used on the '67 C28s chainplates?