There was an earlier discussion about this issue - some Griso and Sport owners, in particular, felt there wasn't clearance between the top of the sensor and the alternator. I started an inquiry with Piaggio about this, but with the August vacation the full response has been a while in coming. Initial response, thanks to AF1 Racing, is that they were able to check on the later Norge and found no problem - they haven't checked a Gen1 yet, last I heard.
In any case, you need to address the issue of the connector on top of the new style sensor. The old one uses a nail-head connector, while the new one uses a spade connector. With the limited clearance, even if the new sensor is a fit, a flag-style connector is the best way to tie in. See my thread at
http://wildguzzi.com/forum/index.php?topic=77673.0 for more information.