The type of belt you have differs from mine, but I have seen the middle loop mounted in the anterior portion of the wood trim.
The belt is anchored on or near the parcel shelf, comes forward through the middle loop, and then also anchored down low by the driver's left hip.
I am not sure what that threaded hole in that flat metal piece is for.
Nor am I sure what the hole is for high up in the wood trim.
Do some searches for seat belt posts, and I know there are pix of this mounting scheme.