The Cinquecento Abarth kit as made by Zender were just add on skirts for the front and rear bumper. The Lester Abarth kit was essentially a copy as far as I know, so again you need the original bumper. The kit fits in the groove in the centre of the bumper.
Just bought a new front bumper from Fiat, was 110 quid, ouch. Then chopped the centre out of it to fit the Abarth part.
Pete