Yeah the SG shaft was a problem for me, but Wolfgang gave me some good knowledge I'll pass on.
1) Flywheel: I use is a wolfpack radicials, but you can use others.
2) Length: You need an ofna clutch nut kit to make the sg shaft long enough. It cost less then $10 and can be found at towerhobbies or your LHS.
3) Clutch: I had the HPI Racing clutch but it wouldn't fit around the clutch nut kit. I dremeled it to make the hole bigger, but decided against modifying the clutch. So i just bought a Ofna 3 shoe clutch and used 2 of the shoes. A mugen clutch will work too.
Hope that helped!