You know the black plastic deflector that directs air upward from the center of the console to the top center of the dash for defrost/defog?.....well it is not connected at its lower (inlet) side. It appears to be about 2" shy of connecting with another plenum box.
Is this one of those expandable plasic or paper tubes that is to connect it? :crazy:
Not familiar with C3's, but C2's (and all other Chevrolet products) are designed with a gap between the defroster outlet on the heater case and the upper defroster duct to isolate the two; if they were connected, the noise and vibration from the heater blower would be transmitted to and amplified by the upper dash panel. :thumbs:
I recently had my dash appart to do the heater core... and I dont recall any ducts actually not touching. Some were kind of loose... and the one you mentioned might be the one that had a POOR fit in mine as well... I did duct taped one of the bad fitting joints! Just a wrap or two...! I did take some pictures, but that one got by without a snapshot! Sorry!