Welcome
@rayinfe to SBO.
sailboat data might help.
The VINYARD VIXEN 29 was also available with a yawl rig.
sailboatdata.com
Here is a review of the boat.
Since 1974, Practical Sailor’s independent testing has taken the guesswork out of boat and gear buying.
www.practical-sailor.com
The SBData suggests the Vinyard Vixen was equipped with a Westerbeke engine. You may find a manual for your engine here. Look on the engine for a model number.
www.westerbeke.com
If you are searching for a operating manual much like a car, I‘m sorry to inform you it is likely an empty search. The concept of a boat owners manual came about in the late 80’s when many new folk to boating were beginning an adventure in boat ownership. Marketing folk told boat builders you have to offer an owners manual like car manufacturers. 40 plus years ago buyers of boats had grown up around boats. They understood that the boat hull was pretty basic. Sailing was something you learned by going at a marina or yacht club. The systems on a boat ( plumbing, cooking, electrical, etc) were all add ons made by outside vendors and sold to the owner by the dealer or as an option by the manufacturer. These add ons were not always sourced from the same vendor. Vendors came and went. Any manuals were what ever the vendor gave to the manufacturer.
My boat, built in 1974, was much the same in regards to lack of a manual. I sat on the boat and identified each of the systems, model, serial number, etc. Then I searched out the manufacturer and in some cases found a manual. In others not so lucky. Since my boat like many used similar radios, propane stoves, compasses, i could use say a Hunter manual for the stove in my Cal 35 C.
Make you own list and maybe we can help steer you to some of the equipment manuals that have survived over the past 40 years.
Congrats on your new to you boat.