Looking for the name of a part, and for the part itself! (74 Fury)

Hi C-Bodysts,
Again with the French Fury. This time, a part is missing. On the firewall (vehicle cabin side), there is some kind of door or trap that closes the blower motor location next to the heater box assembly (engine bay side). Please have a look at this pic, it will be helpfull : View attachment 415135
The pic shows the wide round "aperture" or "opening"on the vertical firewall, where there probably should stand some kind of door or trap, and at the bottom, the carpet of the...

Looking for the name of a part, and for the part itself! (74 Fury)
Author: Seb'74