> Air pumps were for catalyst efficiency. The old ones needed extra oxygen molecules floating around for the big stuff (hydrocarbons) to oxidize with until the catalyst was up to operating temp and working at peak-ish efficiency.

My experience comes from driving and working on a 1988 GMC 6000 truck with an anemic 350 small block with a Muncie SM465 behind it. There was no catalytic converter, only a muffler. It featured not one, but two air pumps, each feeding a set of pipes that led to metal tubes which entered the exhaust manifold opposite each exhaust port. Another odd thing about that truck was it had a choke lever, something I thought was long gone by 1988, and was a pain to start in the winter.

Perhaps other vehicles had a cat but this truck certainly did not.