Linear bearing system

Hmmm... seems unnecessarily complicated...

Assuming the orientation of the slider is as shown in the beginning (and end), the roller on the bottom that contacts the flat bar is not a load bearing part. The flat bar, when welded to the angle, will stiffen the angle to keep it from spreading. If there is any inaccuracy or weld distortion, the bottom roller would bind or be loose. So - that roller is not needed. If that roller is not needed, then the funky welds on all-thread aren't needed either. Also, by removing the bottom roller and that plate, you make it possible for the angle and flat bar to sit on something. If you want to span a distance with the current device, you can only support the ends.

If you were worried about the carriage bending under load, it could be reinforced with a bar across the front and back to keep the angle from splaying.

If you are worried about the moving carriage coming off, a simple J hook on one or both sides would keep it on if there was any vertical motion (based on the load on the carriage moving - say with operations that load or unload the carriage).

Linear bearing system - video