I am not aware of any 3D models of the Duet 0.6. However, I and others have published designs for enclosures on thingiverse, and you can get the critical dimensions from the Open SCAD source code of those designs.
Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod
Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
