Twin extruder height adjustment

I have experimented with twin extruders on my OrdBot but I have not satisfactorily solved the problem of getting the nozzle heights (Z axis) the same. I am using two Jheads with bowden tubes fed from static Wade extruders (1.75mm filament).

I am looking for a few ideas for a simple mechanical adjuster that is easy to fabricate.

You could try shimming the support bracket.
Have you run a dial indicator over the surface of the bed to verify that the X, and Y are square.
J-Heads are quite long, maybe thermal expansion is coming into play.
Are you running two different temps.

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.

Reprappro extruders have a setup whereby the hot end is attached to the x carriage with a couple of screws with springs on them. Vertically, it's X-carriage - spring - extruder body. Height and separation between nozzles is adjusted by tightening / loosening individual screws. They get three individually-adjustable hot ends on a single x-carriage with this setup.