MK2 balljoints wont fit straight in MK3 bones, but they will go in with slight modification to the holes, IIRC its the middle one that has to be made a wee bit longer.
Only issue with MK3 bones is the MK2 anti roll bar wont fit the MK3 bones, but it WILL fit on Passat bones

Also, you need longer driveshafts & MK3/Passat track rods, and I dont think MK3 driveshafts fit MK2 hubs either!