Some cars had an ignition rotor that had a shorting mechanism built into them. As the engine speed goes to a certain limit the piece in the rotor moves from centrifugal force shorting the ignition and giving a mechanical rev limiter. I have seen them on older BMW engines. Maybe Alfa had them in '87.
Which belt needs changing? The water pump belt: loosen alternator.
The ac belt: Loosen and then remove the tensioner pulley
leaving the stud poking through the backside.
Then install the new belt,slide the pulley up from the
bottom, install the washer and nut and tension as needed.
(removing the pulley just makes it a bit easier.Less fight)