I recently lost oil pressure on my 2001 GXV390 and seized the piston.  I was looking at eBay and they are selling a 16hp upgrade kit for the GX390 that includes the 90mm piston and (I believe) the 66mm stroker crank.  I have figured out the piston and rod will work after grinding off the splash tang, but my question is can the stroker crank work in my GXV engine?  Or are they not able to accept the extra gear and bearing the GXV needs?  Are the GX cranks shorter or something that keeps them from being used in a GXV390 engine?
Geoff