Greetings!

To answer your question about the dual fuel pumps, all I know is that the in-tank pump is really just a "lift pump". Since the external (high-pressure) fuel pump cannot generate sufficient suction to draw fuel up and over the top of the fuel tank (where the fuel line connections are), the in-tank "lift pump" was a way to overcome this challenge. It serves to scavenge fuel from the sump in the bottom of the fuel tank and push it out to the intake port of the high-pressure FI pump. For some reason, the makers of some earlier EFI cars either could not or WOULD not (there might have been some DOT regulations that prohibited this or some other design challenge) put the high-pressure EFI fuel pump inside the tank (which is where almost all of them are now). Alfa was one such maker. Ford did this too on some of their early EFI cars. In any event, the dual fuel pump configuration was not exclusive to Alfa Romeo, and it was not done just to be "different" - there must have been some reason for it.

 

My question is why did Alfa use 2 pumps.

Here's the short version.
For 1977, Alfa switched from a bottom discharge fuel tank to a top discharge tank. The bottom discharge tank fed a single fuel pump by gravity but in the top discharge tank, the single pump was also tasked to suck the fuel out of the tank as well. Two years later, Alfa issued a recall to cure driveability problems under certain conditions that were the result of fuel starvation. The recall entailed installing an in-tank fuelpump to ensure an adequate supply of fuel to the main pump.

 

Thank you.To get the fuel at the bottom of the tank. Now to fix the mess. They even used sheet metal screws to mount the unit to the tank.