It looks like I cut the spreader bars out... but in reality, those were not the actual spreader bars, they were merely drill guides. Those tubes were 1 size over. The actual spreader bars will fit through these short lengths of tube that I have left remaining on each bracket, and which I have now drilled through. I did not want to permanently solder the spreader bars in place, if I can avoid it. If I could tap them out, and screw them into the final assembly, then I could more easily reuse the brackets if the need should arise.