Print the shuttle and endstop attachment of choice. Clean up all the supports.
Insert the heat-set inserts, they need to be flush with the surface and reasonably accurate, focus on getting the angle right. There is an optional -thruholes version that allows to slightly thread in a screw from the back to make the angle perfect. If the toolhead does not roll freely, you might need to redo this.
Screw in the bearings, using 8-10 mm screws and washers. They should lock in quite tight, optionally can add locktite for extra safety.
Glue in the magnet. It should be flush or slightly recessd.
Print the back plate. Use a 3mm drill bit on slow speed to clear out any loose overhangs from the rod holes.
Cut rods to length and push in, they should slightly extend past the plastic. I'm adding some PVA glue to the holes to hold them but still be able to remove if needed.
Thread in 2 m8 socket head screws at the bottom. All the way in should be too loose, back up both a bit at the time to get a snug fit.
General rule of thumb - the tightest that runs well. There shuld be some back pressure when clicking together. But not much more than the weight of the hotend.
When clicking together, both bolts should contact the bearings simultaneously. Them being off too much will cause some unwanted twisting loads. I have not paid much attention to getting this exactly right and have not had any problems.
Final step - add a drop of CA glue at the base for the scew head to lock it in place.