Ok, I was asked about doing the GPX fly wheels. I cant answer those questions cuz I have no time with a GPX. Here's the deal, I use a old Honda crank end and bolt the fly wheel to it so that it runs 100% true.
So if a GPX fly wheel will bolt onto a Honda CRF50 crank halve correctly, then its a go. So do some research and ask around before sending me any other brand parts please.
They will bolt right onto the Honda cranks. No problem there. They can also be used in place of a Honda flywheel in a pinch. But the weird thing is if you put a Honda flywheel on a gpx you will have to space out the pickup about 2-3mm to make it fire. Just a little fyi.