The air pump was a fiddle to get around the emission regs that started in California in the '70s. I think it worked when the engine was cold by pumping air into the manifold thus diluting the gases. I've not seen one on an Alfa but the ones I have seen on Jags have a belt driven pump on the engine feeding air via pipes into the inlet ports, the system also consists of various valves to cut off the supply when no longer needed. The egr system and carbon canister were added to the system later as the regs got more strict. Sounds like a bit of research might be the order of the day to find out if your car had it because it was a California car or because Arizona cars had it by '76. Best of luck with it.
By the way California Jags had catalysts as well by then with an extra speedo cable wich drove a hidden "catalyst counter". You might look for evidence of of that too which would confirm it as a california car.
Working from 35 year memory here so don't take all as definite fact!
