Hei.
To be honest, I have noe idea what you mean (or any other´s as well) when speaking of arch work, grinding arches and so on. I may know it, but can´t understand the English phrase. Is it due to the width of the wheel that won´t fit the arch? Is it the body that needs rework, the metal part or plastic inside? I have never had any trouble with this, but have read many post conserning it, but never understood what it was about...
But best way (as I did when mounting new tires and rims with spacers) is to go to a shop, make them fit a tire to an alloy rim and test it on your car outside their shop.
Morten.