oops serves me right for not reading the whole thread.
whatever you do don't ride with a brake that rubs your tire. You'll eventually wear through the sidewall and have a blowout. A blowout at speed on a front tire is something i'd wish upon anyone.
If you want to use that shimano brake then you'll need a drop bolt, or will need to lengthen the slots if there's enough material
personally I'd get a new brake
a tektro R556.