I as thinking of the suggestion that Brandon made of making the motor mounts so that they could be removed from the top beam and remounted with good accuracy.
I’ve also been thinking about mounting them to unistrut using normal unistrut bolts.
The mount below is my idea for dealing with this. It can work with both 2x material and unistrut (once the appropriate holes are added to the model), and doesn’t depend on the bolt/screw being super-tight to prevent it from creeping down the beam. I also added a little height so that there can be a bolt through it and have the motor clear the bolt head
it does mean that there would be a left and right motor mount instead of just one part used on both motors