yes, the screw holes on the original ears and chassis should be symmetrical so you should of just been able to unscrew and rotate then screw directly through the original metal ears
don't mean to knock the design but the rack mount ears can be screwed on to the UDM in a different orientation facing the wall, you can then use these holes to screw onto the wall
Did you use knurled inserts with this? It printed great. Granted for some reason I didn't remember to print with 6 walls (did the default 2 with supports)