Well, you've actually got a bit of a special rifle there. It's nothing super-exceptional, but it's MO marked, which, IIRC, indicates that it's been dated twice. If your son wants to pop a PU on a Mosin, it won't be accurate to put it on this one. If anything, you'll want to put a PE scope and mount on this one. Generally, the PU scopes (as seen in the movie, I believe Vasili actually used a PEM in real life on a round receiver) would be seen, more often than not, on the Izzy 1943 and onwards. Is there a second date anywhere on your receiver or barrel? Some of the MO marked Mosins carry a second date (usually a two numeral code on the barrel, near the original date), indicating when they were integrated into the armory of the "Ministry of Defense." You should also be able to find a date on the rear tang near the safety/cocking knob, as well, to further match the receiver and barrel. Judging from the markings, though, this is just a run of the mill Soviet Tula Hex Receiver 91/30, still a great gun, but not as spectacular as I made the possibilities.
But, yeah, for a truly accurate representation of Vasili's rifle, you need a more "run of the mill" Mosin than this one, like the $70 bargain bin rifles you see everywhere. Yours is a bit more special.
Edit: tater beat me while I was typing! BAH!
But, yeah, congrats on a great find.
Edit, again, upon further examination, these are loafers. I kid, Simpsons reference. But, yeah, looks like a 51 on your barrel, which should indicate that the Russians moved this rifle to the Ministry of Defense in 1951.