This morning I also got the player's gun inventory showing up on-screen. The upper left and upper right guns represent what's in his hands - slots 1 & 2, and the line of guns on the bottom are inventory slots 3, 4, 5 & 6.
The interface for switching guns & weapons in & out of hands is pretty simple, and I believe unique.
You hit two number keys in a row to make changes :
1, 2 or 2, 1 - swap weapons in hands 1 & 2
1, 3 or 3, 1 - swap weapon in slot 3 to left hand
2, 5 or 2, 5 - swap weapon in slot 5 to right hand
1, 1 or 2, 2 - put away weapon in that hand
1, [del] - drop weapon in left hand
Next is to get a background graphic in there, and the numbers drawing on top of the slots.