I spend some time in the saddle of an M2 and really really liked it. IMO the seat and rear fairing were a little gangly but wow! so comfortable for 300-400 mile, really fast and twisty rides. The M2 is still a carb bike, but thats its trick. SUPER easy to work on.
Haha
Its at least a 20 year old Harley based bike. You WILL be working on it, and buy some damn JIC screwdrivers!!!
I'm certainly no expert on the tubers (or anything really) but I understand they still have the earlier Harley engine cases. That means they have a 'trapdoor' for the trans and you can put in a 6-speed easily. I DO know a XB suspension and brake swap is really easy (need a triple tree pivot tube).
I borrowed this from the original owner and rode it about 3500 miles in 3 weeks all around the PNW and Canada during the last eclipse. It has the 6-speed and the XB conversion.
If I was to buy one. I'd get an S3T and I'm sure I'd be happy FYI, I love this forum for all things XB, but I go to BadWeb (Badweatherbikers.com) for expert tuber and Uly info