The alternator on the little Fiat was making a horrendous noise, so i decided to remove it and take a look and as i suspected, both of the bearings sounded awful.
The alternator is part number 63320034 and is a 55A Magneti Marelli one. I did do some searching but could only find aftermarket makes or second-hand ones so i decided to strip it and get the bearing numbers.
If you are replacing the bearings on a Fiat Cinquecento Sporting Alternator 63320034 these are the bearings you will need.
The font case bearing is: 6203ZZ NSK Shielded Deep Groove Ball Bearing 17mm inside x 40mm outside x 12mm wide
And the rear one: 6201-2Z SKF Shielded Deep Groove Ball Bearing 12mm inside x 32mm outside x 10mm wide