If you go the shimming route, I'm not sure how much of the steering box is in contact with the K-frame other than where the ears are but I would use large diameter fender washers or the required thickness of flat stock to spread that clamping force and torque across at least as wide an area as the box contacted before to avoid any potential for cracking.
Thanks. The boxes mounting flange is on the opposite end as the coupler. A small shim at the flange should equate to a larger movement at the coupler. I've got some scrap 20 gauge sheet metal. I thought about making a shim/plate out of that. Then it would cover a larger area then a washer.
