Okay, I just saw X3 and I don't think Belstaff made Logan's jacket. All the jackets on the Belstaff site use spring snaps and Logan's used regular snaps like on most real(not fashion) motorcycle jackets. Maybe Mantis can verify this on his Belstaff. Also Scott's jacket wasn't a custom job, just one of their regular jackets(the racing blouson) in colors other than the one shown in the online catalog.
Other than those things, it seems it would be pretty easy to make the jacket off of a Vanson or Bates pattern. The back design looked to be the same and everything else is pretty close. The big thing would be to get the arm stripes the right width. The only other thing I saw was a seam that can't be seen in any of the stills I've seen(but I would need to look again) that runs from the collar across the upper chest like a baseball shirt and around the top of the sleeve similar to the shoulder caps present on many of the current racer jackets out right now. Nothing really fancy, just lookes like a simple line of stitching. I hope the description makes sence. If not, you'll see it when you see the movie.
Gotta say, after seeing this jacket in action, I really like the base leather jacket. The leather looks really nice, even better than the other two. I just hate that they got rid of the other details. K