Tony,
First, BMC in Santa Cruz had moved to Soquel Drive (off Highway One) by the 80s, but is long gone now. There are people still around who worked there but I can't imagine they could be any help, or possibly even remember a particular used car from 30 years ago. Anyway, its probably a false lead as Santa Cruz is a big enough town in its own right and not that close to Monterey. It's not typically referred to by Northern Californians as "near Monterey" rather than by its own name.
Second, The franchised new-car Jaguar dealership in Monterey still exists as Monterey Jaguar, now in the adjacent town of Seaside. I seriously doubt they could help, but why not just Google their contact info and give them a call?
There were no other Jaguar new-car dealerships anywhere near Monterey.