I've updated this post to include pics hosted on so-called TinyPic instead of Photo****It. Please can someone overwrite the existing post (with broken photo links)?
Here's the original fitment alternator, Fiat part number 46404424 but with a Magnetti Marelli sticker showing model number 63321426 (and type A127IR-100A)
First remove the 3 thin 10mm nuts and remove the black plastic rear cover
The regulator is the black plastic assembly at the bottom, the rectifier is the fancy metallic assembly at the top/sides
Remove the 3 small bolts/screws holding the regulator in place (from L-R medium, long and short, use a suitable screwdriver apart fromt the long one where a 6mm socket works best) as well as the nuts/washers/collar on the main alternator output terminal, and the 8mm nut on the right side
Close-up of the regulator with bolts/screws removed
Remove the regulator, exposing the slip ring
The brushes are clearly visible from below
Carefully slide the brush cover away from the regulator assembly to reveal the brushes
The rectangular brush covers at the edge can be unclipped and removed to reveal the wiring connectors to each brush
Spare parts are available from Wood Auto Supplies where the regulator (aftermarket or Magnetti Marelli), rectifier and slip ring is available, but not the brushes, although they can be found by searching on alternative alternator model numbers, eg: Lucas.
Re-assembly is the reverse of removal, except that the brush cover needs to be clipped on after the brushes are eased over the slip ring.
Push in the first brush as you slide the regulator over the main output post and smaller post on the other side
Push in the second brush as you ease the regulator assembly further down
Push down to seat the regulator, making sure the brushes line up with the slip rings
Clip the brush cover back on and push home with a "click"
Then replace the medium/long/short bolts/screws, the nuts etc. on the main output terminal, and finally replace the rear cover and 3 nuts.