On p. 59 of the R2 manual, v. 1.3 beta, it says: "Take the printted endstop mount and an endstop and secure it in place using two M3x20mm screws and two M3 nylocks."
Does anyone know where "in place" is?
I used 10mm long screws. But make sure the screws engage the nylon in the nylock nuts! Look at the picture to see how to attach the stop to the bracket. On mine I cleaned out the holes and chamfered the corner of the bracket where it got too close to the puns on the back side of the board.
The endstop switch should fit onto the 3d printed plastic clip. I think I put mine with the pins of the PCB into the printed object. The endstop then get clamped over one of the Z smooth rods. Clamp it between the bed and the top of the from at the desired point where it triggers and the nozzle is at the right height.
I would highly recommend printing another endstop once you get up and running. https://www.thingiverse.com/thing:2304434 is the one I am using. You put a bolt through one of the holes ACM bed and you can fine adjust the level by altering height of the bolt up or down.
That's a genius solution and simpler than mine.