I had to cut a small notch out of the side of my ARB mount to accommodate my toothed belt, but only because mine is a conversion from a GT and didn't have the g40-specific arb mount bracket. If you're having that much of a problem perhaps your engine isn't sat right in the bay? If you loosen engine mounts it is possible to move the engine away from that side using a pry-bar and then tighten the mounts again. Or another possibility is that you have a bent chassis leg.
