I’m wondering about alignment and compliance. The metal tracks are going to be mounted on a wood platform. Wood is not stable. It moves around, shrinks, expands, and warps, with time and moisture (read much more about this in Hoadley’s “Understanding Wood”). That means that no matter how careful you are to align the two tracks, they’re going to go out of alignment.
So I’m thinking that the trolley needs a feature it seems to be missing at first glance. The top corner away from the electronics should not be rigid, but instead have a hinge. This hinge should be oriented with its pin parallel to the tracks. This hinge allows the tracks to not be parallel in the X-Y plane. It allows for some compliance as the trolley moves along the tracks.
If the tracks go out of alignment in the Z plane, that’s not a huge problem. It just means that tool head will go slightly out of alignment. Not a big deal, because there won’t be any binding, as there would if the tracks aren’t parallel.
The hinge should probably be made using ball bearing, so there is no play. You don’t want any play with these big moment arms.