Does the derbi stator bolt on tho? I thought they were all 90mm?
if there's a thing that works fill in some details! because I've only encountered speculation on what will work, and then nothing actually works
the 80mm stator size on the 504's not that uncommon (CEV size?). Minarelli, garelli are that small. but the taper doesn't match. I suppose you could do the v1 HPI stator with puch HPI bell
and for sure any minarelli sized flywheel could possibly work on the 504 stator with the 505 crank taper.
I'm very interested in what would work, even though I'm not trying to do it myself, just so people know. I also just wanted to dispel the "oh you just slap it in and put a puch HPI on it" myth