Is shimming a power steering box an acceptable thing to do?

My 68 Dart is going in to have the frame connectors welded on. I want the car on its wheels while this is done. I'm making it a roller...then it will come back apart when it goes in for paint. I installed the steering column so the car can be moved more easily. The stock steering coupler just barely hits the TTI shorty headers. I can still turn the steering wheel but the 4 corners of the coupler seal retainer rub one tube. My first though was to just trim a little off each corner of the coupler retainer but then I thought about shimming the box. It would only take a very thin washer under the box on the inside bolts. I could dent the tube but don't want to mess up the coating. Thoughts?