Picked up my parts yesterday after a ~2 week backorder and installed in my '21 MY last night (original delivery date 6/2021). Installation was super easy, took about 1.5 hours in total as the car already had pre-drilled holes from the factory. As
@BreatheEasier mentioned, the parts I ordered were all correct and are listed below to help make it easier to order:
1) REAR APRON, HEPA,MY (1619812-00-B)
2) HEPA, DUCT,MY (1499137-99-C) - see note below
3) HEPA FILTER (1495167-00-B)
4) Two M6x40mm stainless bolts and two 1-1/4" stainless washers from Lowe's
Note: For item #2 there has been a lot of back and forth on which is the right part number. 1499137-99-C is listed on my invoice and duct packaging, however printed on the duct itself is 1499137-00-C (see attached photo). So they seem to be somewhat interchangeable part numbers at the moment.
As others have noted, airflow is definitely reduced when drawing outside air into the MY. I have to bump up the fan speed two levels (ie, 5 to 7) to get a similar air flow as prior to the upgrade, but the noise level remains low. Recirculated airflow remains the same. Overall this is a great upgrade and would highly recommend to anyone to fix the defective air inlet duct in the original MY design. Thanks everyone for your help getting this done!