the 180 rear adaptor will fit the 170mm...
the 180 rear adaptor will fit the 170mm rotor?
Just a guess here, but that doesn't seem like it would be the hot set up. It would probably sorta work, but since the 180 adapter sets the caliper further from the axle, I think the pads might not get full contact with the rotor. The result of that would be poor braking and uneven/fast pad wear. What 170mm rotor are you rocking? Magura?
Brake track is very crucial, so caliper placement is important. 5mm shims may work on a 160 setup- if you can't find the correct adapter which I suggest.