I think this is a MKII. It's early 1980's given to me by my neighbor shortly before he passed away. All I did was clean it. I'm leaving it worn. The knife was a gift from him too but it was so badly worn I had to restore it to be able to use it.
Your gun looks like a Mark I, actually just called Standard at the time it was made. If it had adjustable sights, it would be a Target model. The Mark II had several improvements to this original design, including a bolt stop lever, relief cuts ahead of the bolt ears and a 10 round magazine. The butt plate visible in your pic looks like it might be an original 9 round mag with the crimped on butt plate.
My Dad had one. I, personally, prefer the Mark IIs, because I think those improvements pretty much perfected the gun.
Here is my small collection of .22 semi-autos. The 4 Mark IIs provide a variety of different shooting options, and that SR22 is my bow to modern semi-autos. I do like the DA/SA trigger, and would carry it in Condition 2 for self-defense (IF New Jersey would allow it).