Although the printed bushing block was a good idea and may be functional with a bit of scaling, the wiggles have made me reconsider. After inspection, I found that the diameter of the bushings had increased just slightly, but enough to allow play. I may try to print out the actual bushing part with igus tribo-filament and somehow marry them to a PLA block. Meanwhile, I am swapped out to the measly 150mm again... However, the frame looks nice and the whole thing is super stable!!