215435 = Darrin air cleaner
207775 = Rubber ring that fits to the top of the air cleaner. It is the same as the rubber horn ring spacer for the 51-3 cars and is available from the club manufacturing fund.
212759 = Dry type element. For this, take the air cleaner to your local NAPA and fit a lawn tractor air filter. The original element had a mesh outer cover that I believe is the same as concurrent GM. The attached pic shows a Chev truck air cleaner with the mesh unit I'm talking about. Find that and fit it over the air filter and no one will be the wiser. And, you'll have a much better air filter in place than the original unit. I did that with my Darrin.