Big Pard and Buckslayer, you guys seem to be correct about the model.
It must be a Grade II, not a "Mk II".
Here are some pics of my new-to-me rifle, exactly as it appeared when I bought it. I haven't cleaned or polished it as yet and I'm hoping to get out to shoot this weekend - if I can get my chores done
I've ordered a Weaver 2.5-10X50 MilDot scope and a set of rings from OpticsPlanet. Hopefully, it'll be here before the weekend. Meanwhile, it has a nice Williams adjustable sight - but I have to look closely to see how that rear sight is attached to the barrel...
The serial number is 137PY08xxx making it an August, 1982 build, I think.