Not sure on measurement differences between 556 and 308 lowers but on a 556 lower you would be OK. The mag release button wont reach the hole, will still slide in channel through full motion. It’s just gonna have a hole where something could possibly get behind your mag release and lock it up.
Install mag release and see if it reaches hole before releasing mag.
Call it a water drain and play it off!
ETA- Just noticed there is quite a variation in the thicknesses of your fire control pocket sides. I would be more worried about this. Your hammer/trigger pins will probably walk. Some KNS or simliar may be needed if your hammer will even make contact with the firing pin an acceptable amount of off center.
I did a 556 pocket a little off center (side to side, less than in your pics) & it walks pins.
Pocket should be in the middle. Even looking at the drawing in the background of your picture you can see the dimension showing equal distances from the centerline to the inside face on each side.
Hard to tell but will the trigger even sit in the center? Is the trigger opening aligned with the centerline of the receiver?