I have not tried shimming. I was really looking for a simple screw adjuster.
I mounted the twin extruder plate on slots so it could be tilted side to side across the X axis. The idea was to allow adjustment of the relative heights of the two extruders but it is not very satisfactory.
The OrdBot has a pretty rigid frame and I have squared X and Y axis using a set square. I levelled the bed relative to the first extruder using a piece of paper under the nozzle in four corners. I then tried to adjust the second extruder height to make it the same as the first but not very sucessfully.
Both extruders are Mk V BV Jheads which are the shorter version. Both run at 235 deg C on ABS.