air duct closure

I am still fiddling around with my heating system.
To correctly install the '76 heating I need to connect the passenger side heat exchanger with the heater blower in the engine compartment.
For this purpose, I need to close the passenger side air outlet of the fan housing.
Does anyone has a part number for this famous closure panel?

Thanks, its going to freeze outside.

Jens
('76 CIS with '73 body conversion)

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