........but not "that" special, that we can expect the general public to respond here to a thread.
It's a big world out there, lots of boats, however there were relatively few XK boats built, and fewer yet survive.
In addition, your boat looks like it has relatively low hours, which means the people out on Arrowhead (or any other body of water this boat was on) may or may not have ever gotten a glimpse of it, because boats can go out for a run and other people often don't see them or care, and if they did see it they may or may not have had a CLUE what they were looking at, and if they did it may not have become a lasting memory. In addition, the chance that any of those people would have found a thread here, despite the millions of page reads this forum gets each year, is slim, and subject to pretty much "chance", which in probabilities is generally thought to be five percent. Then if they did see it, they probably didn't run the owner down and log in his name and address, lol, so enjoy the boat and hope for the best. So there is a "chance" that someone on this forum will, indeed, know the boat, but its going to be like a lightning strike.
You can contact the California state records and hopefully if you find someone who is kind hearted, and will actually GIVE you the name of a previous owner, then that might be productive. In addition, the person who sold you the boat surely knows who he got it from, and that is where I would focus my time, on the phone, with email, and with snail mail whatever it took.
I might add.......although the boat was on Arrowhead, there is no assurance at all that it was actually on that lake much, or for its entire life, as these boats do get around on trailers. The one Jim Peters has on the West Coast in Seattle came from New Jersey.
The photos, by the way, are spectacular, you got a good one.