Good eye, Jim! It's a K4.
I do believe that it is the only Mossberg .22 of that vintage that I have ever seen in my life. I had no idea they were so common, they were not common at all in the area I grew up in.
Now I live in Indianapolis where there is near as makes no difference no used gun market and the used guns that exist are all fairly new and all of them are overpriced. I think I need to get out of the city. I can take the wife antiquing out in the country and while she is browsing I can hit up the small town gun stores.