check this out (once get past the miata thing its still cool) runs in java.
http://www.miata.net/garage/tirecalc.html
I think I am running 235/60r15's on rallyII's on mine. So your 254/60r15 are not much wider (I assume they are on the frount) and the 275' are on the rear. (they maybe to big) the question is where do they rub? what back spacing did you order? I saw somewhere a guy just running 16x10 rims on the rear I can no longer find it but I have it saved at home, body all stock no rubbing. You may be able to get longer wheel studs and a spacer plate but its hard to say with out the backspacing or knowing where they rub at.