Hey dude! What about changing the plate orientation instead of switching to linear rails?
I saw this video and 3d model can be downloaded... instead of acrylic parts that holds the mirror, maybe a 3d printed support could help ☺️

 

So I made some of my parts, designed them on the 3d printer, but what hardware did you fit between the Y gantry plate and the mounting plate on the outside? I can't get any hardware to fit!