The Y rail involves positioning the Iverntech rail system on either side of the scaffold. This OpenSCAD module that lays out these parts are in, xshuttle_assy_wider(). For this set up the Iverntech MGN12 450mm Linear Rail Guide with MGN12H Carriage Block for 3D Printer and CNC Machine which you get from Amazon is used. It positioned in place using these 3D printed connectors.

Rail connector

There are 3 on either side. It looks like this

MGN 12 rails you get from Amazon

Slider shuttle bottom Slider tslot connector

endstop_y.stl