I understand that they are now using a modified Mustang box as basis for Mopar's. Perhaps they got it right this time,,,,or are you already using the new box,,,was added sometime in past year or so.

Been there, done that on my EBody, including requesting a replacement box from Borgeson which had exact same problem. Got burned good by them for shipping charges on their screw up however. Finally resolved utilizing a 1/4th shim on 2 bolt side.

All is now well,,,,however one tie rod(forget which side is 3/4 inch longer than other to have box at top center. Doubt that this has any effect on drivability.

Subsequently have acquired new correct steering box mounting bolts,,,photo shows grade 8 hardware store bolts.

In my case, don't believe was sector shaft. If your steering shaft makes an angle just before entering coupler as mine did,,,,it's likely that they did not jig box correctly before welding mounting ears.

Your shaft should be a straight shot to box from firewall into Bergman coupler,,,just as with factory box.

Not to suggest that your pitman shaft could too be mis-machined.

Overall a PITA with a lot of finger pointing and replacing the box to try a new one and then replacing again to re-install their original once I decided to do the shim approach.

All is well now, do like the drive.

Also installed one in the wife's 55 TBird. Had to adapt a full size Ford Borgeson kit to T Bird as no kit for the Bird from Borgeson. A giant PITA, but worth it as TBird steering system with slave cylinders and all was so bad.