Hi Eric: Yes , there ought to be a plate here to mount the body to the front crossmember.
Ideally it needs to be a bit wider than your blue square, and finish further back to stop air spilling past the bottom of the radiator.
If the front of the body is loose, be careful not to crack the GRP at the base of the windscreen pillars.
Before you fix it down, try to line up the front wings with the rest of the car, if they are out of line when the under-skirt is in line with the chassis you may have problems elsewhere. If the headlights are the same height, and the doors line up as well, you have won the lottery!