Interesting question, Lonnie.
I'd say the "Original GM Photo", "My air cleaner", and "Mounted on my carb" are R.P.O. 216D
I had never noticed that the optional oil-bath air cleaner on a 3100 with Hydra-=Matic transmission was a different RPO, R.P.O. 216G. I wonder what's different? Maybe the automatic choke gets in the way of the "standard" oil bath cleaner. I'll try to remember to check this later today.
