I'll offer a few observations. The brass bottom plate appears to be from a 1905 Russian Maxim and has the early style number font, but the only way to tell is to remove the grip frame and look at the inside rear end of the bottom plate and see if it has been modified so the sides fit the blow the dovetails. Brass bottom plates were also made for early 1910s, but the two types are different in details. The bottom plate is stamped with the Finn Tikkakoski factory logo and the factory S2 letter and number. This was put on when the gun went through that arsenal. The top cover is dated 1944 for the repairs and engrave with the AV1 logo which was a major repair and upgrade arsenal. This suggests to me that the gun went through a second upgrade in 1944 after its first modifications to the 09 specs.
"Korj", stamped on the top cover, means "repair" and the date it was done is 1944, which is quite late, but during a period when many upgrades were done to Russian 1910s. At that late date, upgrades usually included additions that were designed into the Finn made Maxims, the 09/32 and 32/33s. These features were not used on earlier modifications of the 1910s. The specific feature are added plates on the sides of the feed block cutouts which was a Finn design feature of their own manufactured Maxims. On the Finn made Maxims, 09/32s and 32/33s, reinforcement plates were also riveted around the slots in the side plates where the recoil/crank assembly moves back and forth. You do not provide any pictures of the is area of your gun to show if these reinforcement plates are assembled there.
The use of the bottom plate serial number on other parts suggests that the gun was still assembled with those original parts when the Finns got it. The 09/21s typically were upgraded from early smooth jacket Russian 1910s simple because the adaptor for the tripod mount fit the smith jackets much better and more solidly than when used on the fluted jackets. the small stud on the bottom of the jacket located the mount adaptor. The witness mark numbers for the alignment of the jacket and the trunnion are 27, the last two digits of the serial number.
The Finn adapted shorter rear sight has the serial plus the Tikkakoski logo on it, and the forward slot from the old Russian rear sight is still there. The Finn rear sight is a later addition when the gun was repaired, so they used the original serial form the bottom plate. The serial ison the rear of the top cover and on the top o the grip frame, and appear to me to be Finn numbers,not original Russian Tula numbers.
The original Russian factory ID, date and serial number were ground off the top cover, and would have been for Tula, the first make of the 1910s. The left sideplate has faint remains of another longer number with the current serial stamped above it.
Fusee cover is early interwar Russian 1910 part. Many of these guns were outfitted with Finn made fusee covers usually with the AV1 engraved on them.
Hope this helps.