I modeled this to allow me to make mounting dual tops side by side easier. I did not add the 4 slots to use the hanger accessories. If there is a desire I can add them in. 

I printed in PLA with the top surface down using some supports on the center counter-bore. I suspect it would print fine in the bottom down orientation with no supports just fine with enough top layers. 

Note: The 4 Hole version is a WIP and may not be entirely accurate.