After talking to Lance Gingel in the USA, who is building an RV7, I have borrowed his idea of how to mount the Dynon ADAHRS unit.
This also eliminates the problem of getting the unit level horizontal or longditudinal axis, as the shelf attaches to them at the same angle so you get 0 degrees mounting error in htis plain, now I just need to ensure that I install the unit properly aligned to the perpendicular or latteral axis
Left view of shelf installed behind rear baggage area