400 fourtrax at disc brakes from a rincon

Hey guys I’m new to the honda atv world but I picked up a 400 fourtrax AT and a set of what i beleve are rincon disc brakes for it . The only problem im having is the lower ball joint . Every thing bolts on but the lower ball joint from the rincon has a larger stem then the 400 control arm will accept. The 400 ball joint is smaller where it presses into the knuckle . Anyone done this swap before and know a ball joint that solves the problem ?? Thanks for any input