the alternator could be replaced with a smaller unit (one job I still need to look into), but you will need to make a new mounting bracket and loose the auto-tensioner.
the belt needs to be shorter, something like 50mm less, I can't remember exactly
the alternator pulley is different to the usa version and won't fit, I have a usa alloy pulley sat in my garage (which I will use when I fit a smaller alternator)