In this tread I said that I had built a 1/8th inch thick shim to correctly position this box on our E Body. It should have read 1/4th inch thick shim. The posting is past the time when I can edit this URL directly.
On page 74 of the Mopar Chassis Modification Book it states:
CAUTION:
To prevent over stressing the steering gear housing mounting bosses, do not use a shim pack of more than .090" total thickness.