Adding 2nd arm to a VPI TNT 6

[lem321]

I am designing an arm board that attaches to the left rear tower on a TNT 6, similar to ones used on the Avenger (and HRX) turntables. Can someone who owns an Avenger check some measurements for me?

• Overall width, length and thickness of the Avenger or outrigger HRX arm board;
• Diameter of the circular opening of the arm board and diameter of the corner post;
• Width and length of the gap in the “ring” of the arm board that narrows with tightening of the screw;
• Size of the screw;
• Final finish of the machined aluminum stock - painted, powder-coated or finely sand-blasted?

Would greatly appreciate any help you can provide and thank you in advance for your time.
Below is an early mock-up.