PMK...
Only option is to make a brace to fit the dimension across the pins.. I haven't seen a brace that didn't tweek the front of the chassis.. You're right about tolerances... And the parts do "move" when molded, so you have alot of difference between one arm and another... I don't run a brace because of that problem... One other solution may be go back to the original idea Assoc. had and use the tube that connects the uprights.. That way you can shim it in or out to get the proper length.. easier then making new braces all the time!!! Hope this helps....
Wayne