looks like the supercharger is sold, and that there is a wait list if the sale falls through. to find out what is different about it, your best bet is to contact steigemeier. he is an expert at porting superchargers. the idea behind it is that if the supercharger can be made more efficient then it will make more boost with less heat aka, more power. Steigemeier doesn't really advertise that he works on the Eaton M90 because he caters more to the V8 crowd.
http://stiegemeier.com/