Have a 71 with some engine mods(deletions by PO), no air pump, and the rear connection to it on the air cleaner was just left open,(which left intake of a small amount of unfiltered air).

And the air check valve outlet was plugged off. Ran ok, but was wondering if I could connect the air check outlet to the back of the air cleaner?

You could I suppose, but without the pump it would just make the engine compartment messy. I just plugged the hole (use the search function to find out how...)

I don't know where you could get a new pump, but someone else here might.