The inside and outside teak on Catalinas of your vintage (mine's an '86) were and are different. Topside is plain teak. No one knows what the POs of your boat did with the wood. Could be plain teak, could be varnish, could be cetol. If it's plain wood with no finish, just use teak cleaner then brightener. Then decide what you want to do with it. If there's a "cover" on it, you'll have to do some research to figure out what it is - ask the PO. If he's not available, ask someone on your dock who knows if they can ID whether it's varnish or cetol.
Down below is simpler. Catalina stained the teak. If it's flat (and not varnished over) then teak oil or lemon oil is just fine to keep it looking like new. I used teak oil, others swear by their own other choices. Others like to varnish down below, too, but I hte shiny down below, and figure there's enough work to do on the handrails that more varnish down below is too much work for me.