This very rare option is correct for 1971-72 convertible GM A-Body. Unfortunately pricey but you already know that if you have been trying to find this option. $650 shipped insured in the USA. Included is the fan motor, duct, grill, dash plate, defog switch, wire harness from switch to fan. The previous owner cut the purple wire near the fan at the factory terminal connector for some reason as seen in photo. Perhaps he accidentally pulled the wire out of the terminal and just used butt splice connector. (Easy fix to replace with correct terminal connectors.) The other wad of wires bottom right of the photo is not included.
I confirmed the part number of he duct for the convertible blower in the parts catalog. The PN is 9841740 , used for 71-72, Thanks MO