There are 2 things that you can do
1: Cut the end of the brake arm off that takes the spherical bearing & weld on a new 1 that you then bore/ream out to 22mm to take a GE12 spherical bearing, standard is 22.5mm od
2: This is what I've done. I got hold of a YZ490 brake arm(think 250 is same) which has same issue & needed to shorten it by 19mm to fit so I did the same as above except the end piece isn't just round, the end is pushed up inside the aluminium extrusion & a slot cut to weld through. I can take a shot of mine fitted to the bike if you want
Hope that makes sense
