PS The two stage fuel pumps are pretty common for 80's L-Jetronic cars.
They are assembled as one unit and look like one pump if you take them out
of the tank. The pre pump is a scavenger type pump that fills a chamber
surrounding the main pump. As far as I know the electrics for these are as
for a single pump in that one set of leads is provided and the pre pump
gets its electrical from the same set of leads as the main pump. I don't
claim that the GTV 6 has this type of pump, only that you cannot tell if it
does without a manual or removing the pump. Later Bosch systems used a
single pump.
I know that in addition to the GTV-6 and Milano, BMWs and Peugeots
use the same sort of pump, located a few feet downstream of the tank.
The Alfas don't have any kind of pre-pump in the tank, but I can't
speak for the other cars, because I've never been inside their fuel
tanks.