If I had a nickel for every time I've seen or heard the Standard referred to as the MkI... I usually don't even bother trying to correct it any more, kind of like the grammer nazi thing.As always, very astute of you to mention the Standard Auto is not a Mark I. I kept my lips sealed this time.
And the tight frame fit? That's one of the two issues people struggle to overcome when disassembling and reassembling a Ruger .22 pistol. I tell people, but they don't believe it until they actually see me do it, especially on a pistol that's not been broken down very many times, a big, heavy, hard rubber mallet is often the correct tool to separate and/or reattach the two halves. The more you do it, the easier it becomes. The other issue, although it's already been mentioned, is making sure the hammer strut is hanging just right, to go into the mainspring plunger. When you have been ever so slightly tutored, it's easy to see when it's "just right".
Speaking of the tight frame fit- way back in the day, when I had my first Standard and decided to do something about the poor finish on it (the one I nickel plated), I had one heck of a time figuring out just how to get the top separated from the frame. You see the ghost of a pin that you can see near the front of the frame, that permanently attaches the front of the trigger guard to the frame? I decided that must be what was holding it. Yep, I foolishly wailed the heck out of it with a hammer and punch. Fortunately I realized that it wasn't going anywhere, and stopped before I did any real damage. It took me a little more looking and figuring to get it off the right way. It was incredibly tight and took some hammering with a 2x4 as I recall.
I was young and had nobody to ask, no internet or youtube to consult, didn't know any real "gun people" who would know, so I had to figure these things out for myself. It never occurred to me to actually do as Ruger recommended, stamped right into the metal on the gun itself, and write to them for a free instruction manual.