With many thanks to Stefan Buda,
who very generously gave up his time to assist with the design idea and then provided the DXF files, I now have the Altitude Bearing arcs ready for the next stage.
Stefan also provided advice on the mounting plates and then drew them up on CAD overnight for me
Many thanks also to John Langridge of CALM Aluminium @ Minto, for his excellent service, water-jet cutting them out of 1/2" aluminium plate. I sent the DXF files to John on Monday and had the finished parts in Canberra first thing Wednesday at a huge saving over the local people.