Welcome aboard, Miss Tee/Ollie B! To the best of my knowledge, Wellcraft was not involved in the construction of Californians as early as 1975 or 1977. My understanding is that Wellcraft wasn't involved in production until about 1980.
Some may have been built by Wellcraft on the west coast (I'm speculating here...) but most, if not all, of their builds were somewhere on the east coast. The company was sold to Wellcraft in 1982 according to this article
and Marshall bought it back 3 years later. Carver bought the Californian line in 1987 and in late 1989, moved all builds to Rocky Point, North Carolina according to the article. I'm not sure how accurate those dates are, though. The Californian name was bought by Marshall/Navigator Boats years later and resurrected in the Navigator Californian 39 line.
I had the opportunity to speak with Gil Marshall, son of Jule Marshall, when he was running Navigator Boats. Jule was on speaker phone at the next desk listening in and agreeing with what Gil had to say. In 1977, Gil was a 'bilge rat' working on my 1977 boat at his Dad's company, Marshall Boats. He said he was the kid who laid the wires and lines needed to plumb and wire the boats in those days. He also stated that since they really didn't know all the ins and outs of fiberglass layup, that these early hulls were built extra thick, "like tanks" he said.
Over the years of the company being sold then repurchased a couple of times, they lost track of all the records of the Hull ID Numbers (HIN) which changed format through the years with Wellcraft and Carver. He emphatically stated that one sure way to know if your boat was built in California by Marshall Boats is the first 3 letters of the HIN. All Marshall Boats Californians start with the letters "JCM" and stand for Jule Marshall built in California.
For example, My HIN is JCM034010277.
JCM= Jule Marshall in California
034= 34 ft LOA...(this was later truncated to 2 digits as no boats were built over 99 ft so 3 digits were not needed.)
02=(my guess is...) February build
77= build year is 1977.
I don't have a data plate on my vessel to verify hull #1 but of all the Californians I've come across, the 2 (or 3) digits following the model #/LOA represent the build number in that model's lineup. Also, I've never seen a HIN pattern like mine with the numbers immediately preceding the model year (last 2 digits) that was higher that 12 so this seems to support the theory of the build month followed by the build year.
There are many variations in HIN in other models built by Wellcraft and Carver, but the build year is typically easy to discern near the end of the HIN. Some variations have letters inserted into the middle of the HIN which may represent build number or month.
If you'll post up your HIN and a photo of your brass vessel number plate, we'll try to help you interpret what it means.
You're gonna LOVE that boat and those engines!! I have the Perkins 4.236s which are normally aspirated, 4-cylinder versions of the 6.354. They are very reliable, easy to work on and efficient.
Welcome to the club!!