swinging side to side is not a noticable source of error in the maslow.
if your beam attaching to the sled is vertical instead of horizontal, it will still rack and bind because you are applying force only to one end of it, so the give (and friction) in the mounting will cause it to rack a little bit, which will increase the friction more.
how do these rails ‘stabilize’ the maslow? they move based on the movement of the sled. how do they restrict the movement of the sled in any way?