I have the full complement of clutch goodies from JBS including the extreme sheave.
If you go with JBS ask James what secondary spring and clutch weights he would recommend. He will want to know what size tires you intend to run as well as what kind of riding you do. He'll dial you in first go around.
I also added the wet slug clutch kit (for extreme reliability) and the weights I got from him were Dr OD pulley.
Also told him I wanted a HMF Titan quiet muffler and a PCV fuel tuner, and he hooked me up, and programed a great tune in it as he uses the same setup on one of his rides.
This layout isn't cheap, but you are getting the best IMO.
Makes the bike more eager.
If you were drag racing there is another option through a different vendor, but it's even more expensive.