Based on the initial prototype, which we were actually very pleased with, we went back to the white board and tackled some of its shortcomings. The primary issue we had to address was how was a robot arm or xy-table going to hold on to this thing.
That was when Hunter came up with the idea of supporting the entire paint head from the center with 2" bolts. So we redesigned the tray to hold 9 2" 6-32 bolts. Above these bolts an aluminum disk would serve as the mounting surface. With this configuration any module that consisted of a 40 degree arc with a 3.5" radius, could just snap into place.
As always, here is the final Google Sketch file so anyone that wants to can design this along with us.