Looks like your frame vertexes are a bit smaller than they should be, or the y-parts a bit bigger. There is very little clearance. I made my y-idler bracket at 40mm/s as an experiment. That made it a bit blobby, so I had to file the blobs off to stop it rocking, it is that close.
However, when I fitted the z-pulleys the nuts touch the ground, making it rock again. This is predicted by the STEP assembly model, so it is a design error. You either need to use thin nuts, or put double sided tape on the vertices to lift them slightly. There are also some feet on Thingiverse but they seem a bit tall for my liking.
[
www.hydraraptor.blogspot.com]