[William]

That appears to be the GMPD 302/396 service replacement air cleaner. Sold dozens of those back in my parts days. Production units through August '69 had a flat bottom as noted and the vent tube was 90º. The raised bottom unit was used in production starting about September 1969 for the '69 Camaro and the '70 Chevelle.

The seal flange is also a GMPD service part but didn't need the modification to fit a '70 Chevelle, probably done to use a narrower steel roll and save a few cents. I don't know if it was ever used in production.

The flange extension you have pictured is a cheap repro from the '90s. Does not look much like the original.

The element appears to be a later AC service part.