There are actually two different blowers out there in terms of brand. The M90 has just been 'New and Improved" in the latest version from Magnum Powers, the MPIII. And there is an 1.7 Autorotor twin screw that has been incorporated into a custom made kit. The AR kit is the best bet in terms of hp gains, but is also the most expensive and requires custom tuning, which is included in the price. But there is a waiting list to get one I believe. Another blower kit adapted from the Jaguar M112 is also in the works, but I'm not sure how that is progressing. There were also two custom made kits utilizing a 2.3 Whipple, but they are not being made for sale any longer.
So you really have three choices right now:
Magnum Powers MPII - can get one used as no longer produced. Replaced by:
Magnum Powers MPIII - send in your stock M90 as a core.
AR kit. Waiting time and $$.
Hope this helps!