No, I do not suggest using washers of any kind to space out wheels. The wheels need to be flush with the mounting surface for proper clamping. I've seen guys try to do that with washers, only to lose the wheel from the vehicle.
I did a quick check, ARE lists a 1/4" spacer in their catalog for abour $7 each. Any ARE dealer can get them for you, or you can go to their online store. Here's a pic of the spacers. http://store.nexternal.com/shared/S...;CategoryID=2054&Target=products.asp


Bill Burmeister