If your barrel is marked .308, you are good to go on 7.62x51 ammo as well.
308 Win is a higher pressure cartridge than 7.62x51. 7.62x51 ammo can be safely fired in a 308 chamber or 7.62x51 chamber. 308 Win ammo is above 7.62x51 specified pressure and should only be used in 308 Win chambered barrels. This upper has a BA barrel chambered in 308Win.
Yes - this is the opposite of 5.6 Nato vs 223 Rem.
7.62x51 is the same caliber as a 308 win. So yeah