I did a lot of research on Rugers over the years, and figured I should share the info I've learned since I haven't been able to find the time to make proper, accurate cast replicas, yet..
The upper is from a Ruger 'Standard' based on the sights. And the visible markings make it somewhere between 1949-1965, 'STURM, RUGER & CO.' -vs.- 'STURM, RUGER & CO., INC.' which is post '65. But it's actually not an MK1 at all. The Standard was the very first Ruger firearm ever mass-produced, back in 1949, offered up until '82 or so as a base model pistol. The MK1 upgrade came in around 1950.
The MK1 was just an upgraded version of the Standard, which had better, adjustable sights, longer barrel & a screw in the trigger for adjusting and/or removing the 'slop' in the trigger. All of which was added primarily for target shooting. Otherwise, they shared the exact same parts and manufacturing except the stamping on the left-side of the upper receiver.
I noticed that the lower was switched out (just like Han's ANH blaster oddly enough!!) with either a post-1970 'Standard' lower, or a post-1970 'MK1' lower (which both had a mirrored version of the grip-frame after the '70s)...unfortunately we can't tell for sure from the photos we have access to which one it is. The only difference to the lower is the trigger with the adjustment screw, otherwise the lowers were identical in the factory and used for both the Standard and MK1, just different triggers.
In 1971 they changed and remade the die they used for the lowers, since the dies were getting worn out (the lowers were stamped from sheet metal).
I also suspect that the Lower was from one of the Wood Gripped versions (which are a bit rare), basing on the visible outline 'around' the plastic grips that Bapty must have changed out. The wood grips had a slight difference in radius' and size in certain places, note the outline around the plastic grip here in the pre-pro photo Chris,
lonepigeon kindly posted many years ago..All of the wood gripped versions I've seen seem to fully cover the pin that's partially visible above the top left-side of the plastic grip, right where the outline seems to follow.
As far as I can tell all of the plastic gripped models reveal that pin just as the one below does, whereas the outline around it suggests that the grips were changed out.
That's mostly it as far as the Ruger is concerned. Please don't go buying them all up and start modifying them!! I hate that, and I don't want to be the cause. I know it goes against our hobby, but I really hate seeing all of these antique things being modified and cut up and such.....All the community needs is one pre-'65 upper and one post-'70 lower to study and make accurate, cast replicas from. Please don't use this info to kill off Rugers like the C96 and Graflex. Let's just make some nice, accurate replicas basing on these details!
..I still can't seem to track down what barrel they switched it with..it's not a stock Ruger barrel for sure. It appears to be a pistol barrel though. Basing on the taper it has, a rifle barrel wouldn't be able to taper that steep and keep any length beyond a pistol's barrel's length. Whatever they used led to them turning down the length of the front-end of the upper receiver for it to fit/work, causing the upper to be noticeably shorter than a stock upper-receiver.
-Carson