330 GTC Air cleaner HW question

I don't see any type of washer in the parts manual.
Your concern seems valid to me. I wonder what the purpose would be, as a spacer to compensate for slightly taller air filters? Maybe so, because when you tighten the knurled nut, they don't feel like they are bottoming out, though I never thought it was a problem.

Along the same thought process, the 9 nuts that hold the air cleaner to the carbs should be a nylock to help prevent them coming loose and getting sucked in. I always close the chokes when I remove those nuts...don't ask why.

 

The rubber washers belong under the 3 knurled thumb nuts on top of the air cleaner lid. This is to keep them from vibrating off. Somebody got it backwards on your car. Absolutely remove the rubber washers from inside of the air box to prevent ingestion and damage.

 

Ferrari did not use rubber washers under the knurled nuts on a 330 GTC air box. On a 330 GTC the nuts act directly on the air box lid with no washers. The 365 GTB/4 (Daytona) was the first car to use the rubber washers, with a regular washer on top and then the nut.

 

..., but perhaps not all Daytonas, more specifically very early production examples with 3 nut cover, came with rubber and washer under the nut ?

To OP (todaxyz): Having a rubber and a flat steel washer between the cover and the knurled thumb nut may not be quite OEM correct for your car, but they do provide some protection against paint scraping and can help prevent nuts coming loose due to vibration while driving/running the car.