I’ll need to put some aluminum spacers in between the two rails,

I’ll need to put some aluminum spacers in between the two rails, but I think, so far, so good. One of my beams is 1200 mm and will be cut to 1152.4 mm before assembly. (I cut it 1200 mm when I thought that would be the length of the Y axis beams).

Have a good look at the bearing in that black block some of the Chinese ones are junk!