I have a wrx MY98 converted to 6speed 'box.
I've long wanted to fit a clutch for a 6speed since it should handle more torque without being heavier on the pedal (bigger dia)
Somewhere I read about the starter motor on the OE 5speeds might/might not fit the bigger clutches.
What about it, anybody knows?
Does the inner walls around the flywheel need to be grinded?

 

My understanding is that if you fit the 6 spped flywheel and clutch you then need the 6 speed starter as the flywheel will also have a larger diameter and the 5 speed starter gear will no longer fit the larger 6 speed flywheel

 

Ive just done this on my 1995 WRX. I Did need a 6 speed starter.