I adjusted this to fit when the bed is zeroed. I've made some adjustments, but not tried to print the end result. This version is for a gauge with an 8mm spigot. See the remix for a 10mm version
See also my thing:2587021 for a bridge which will help to check alignment from the Y bearing rods (as shown in the last picture)
Must build with supports, and these take some tweeking (I used 88 degrees in cura) to avoid filling in the screw-holes.
A version with a 10mm spigot hole is here thing:1952482
11 Sep 2017: Seems I was being overly cautious by marking this as WIP - it's my most popular design, and I've had no feedback of any changes needed.