I was able to reach an ABYC electrician I know and he explained the standards; so I will be using a terminal strip inside a covered junction box to extend the existing cable. That wire is definitely boat cable that was commonly used in late 80s Defevers and many other trawler-types. The entire boat is wired with it. I always replace any of it that looks corroded, but this one is bright and shiny.
Thanks again for the advice.