yep the spacers is where you will need to mod. the spacers are made out of some soft metal so you can use a hacksaw and then file down to the exact size you need.
here is where it gets tricky as there are two trains of thought:
Train 1) cut the spacer on the non-caliper side until the rim and everything bolts up. by doing it this way you are not changing the caliper and rotor spacing. But there is concerns that the wheel will be off center within the clamps.
Train 2) cut both spacers to fit the wheel. But you will need to cut some metal out of the caliper mount or on the caliper so that the caliper and rotor can line up.
so choose your train and ride it
my personal thought is to go get the stock ktm65 clamps modded by pax then you are not cutting any spacers or any thing. call donny@pax and see how much it is. it could be only $50 but not more than $100 I believe.