It is hard to tell from the pictures exactly how much clearance there is. The Robart rubber tires have too thin a wall to sand down, so if washers can't hold both sides away from the fork, you may have to go back to the stock GB, foam rubber tires that can be sanded down. I only have a very small clearance between the foam rubber tires and the fork myself and have experienced no ground handling problems as a result.

Another trick I just remembered is to bend the forks together just enough so that they can pinch-hold the axle and wheel in place while you manuever the axel screws in position with a needle nose pliers. A small hole in the pants can be drilled for an allen wrench to tighten the screws. You don't need a band saw to cut the wheel pants if that is what you want. I just used a hand-held razor saw to cut the 1" section out of my telescoping pants for the GP GB. A hack saw would work too, but the hack saw would create more chipping on the cut line because it has bigger teeth than a razor saw.