I found an easy way to get this all glued up, was to take a piece of 7/8 diameter dowel rod and cut it to the width between the handlebar mounts. I attached the lower mounts to the dowel w/ about 1/8in of the dowel showing to give clearance.
Leave the mounting screws loose and sit the mount/dowel/mount assembly on a flat surface and rotate the mounts till they are perfectly flat. Tighten the mounting screws so they won't move.
Attach that assembly to the box mounts, and you can position them wherever you want on the box. Then use the assembly as a clamping point and you're guaranteed to have everything parallel.
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[B]Flat black (dark) member #155[/B]