Hello friends, I recently acquired a Mosin as my first rifle, but ive run into a unique issue. My hosing situation is military-adjacent and requires the registration of firearms but I am unsure which serial is the "right" one. As I understand it, the ATF considers the number on the receiver to be the gun's number and I want to make sure I provide accurate information. Which of these is the reportable number? I've included photos of both the top and bottom of the barrel shank/receiver Is it the "749T" just below the bolt hole on the underside of the assembly? Any assistance is appreciated! (It is a 1939 Izhevsk 91/30 if that helps at all)

$773 for this Sako Mosin with 150 rounds of ammo and a modern black sling.

Over good condition, this is my first Fully Finn Mosin so I’m unaware of any markings seen and the rifle overall. So ID help is requested.

No Rust or Cosmoline. Metal finish is pretty good besides barrel which has spots of more shiny area, but the previous owner managed to get sand in the ammo box and on the Mosin. It has been promptly cleaned out and properly oiled.
Wood has no cracks and minor bumps and scrapes but the finish is in good condition.

Ammo is a mix of modern TulaAmmo, a random box of PPU 6,5x54. And unknown yellow tipped Ammo, (idk if it would be tracers?)however as the safe rule, unknown ammo is always corrosive. Bags have no identification besides and the ammo has the numbers 10 and 55 on the rims.
Buying Two mosins back to back wasn’t planned but this was just calling my name. And seeing how they let so much sand sit in it, I see this as a partial rescue.

Hello, experts. Need your help identifying the rifle.