Lens board for 203mm Graflex Optar

I want to make sure I am on the right path. I have a Graflex Otar 203mm f/7.5 that needs a lens board. I measured the insider diameter of the locking ring and it is 35mm. Is this a Copal 0? I need to mount the lens on a Graflex Pacemaker: which board do I need?

Thanks for your help.