... wondering if you know the P/N for the blue air filter assembly in the photo you posted ...
I inserted that photo into Tim's post.
That is a very common air cleaner assembly for the 335 series engines (351C, 351M, 400). Those engines were manufactured from 1970 through 1982. They were manufactured in two heights, the early pre-EGR assemblies (1970 - 1972) were taller than the later assemblies. As I remember the 385 series engines (429, 460, 370) used very similar if not identical air cleaner assemblies. Lots of larger Ford, Lincoln, Mercury vehicles and trucks were equipped with these engines.
You will not find an original one new. Used versions are available on eBay or via your local Pick-Your-Part (Sun Valley, Santa Paula). The chrome lids are available on eBay too. Reproduction air cleaners for Boss 302 and various Cobra Jet engines are available via the Mustang parts outlets (Scott Drake, National Parts Depot, etc).