I sure do love the Felts! I'm trying to talk my Uncle Phred into having us build a "Bultaco" Felt for him.
There's a few ways to do the tank set up and it doesn't seem very difficult at all!
The FireBelly Hard box is designed w/ jackshafting in mind! It can be fitted w/ 7(ish):1 gearing instead of the normal 4(ish):1, a lower rpm clutch, a longer output shaft, and a right side bearing support.
SBP is working on jackshafting just about everything on the planet. A couple of real Jackshafters!