Figured I'd stop by here before I go to that auction site. I'll measure my board I have it's either 3x3 or 4x4. This would be for a 1941 Graphic View 4x5 monorail cam, which I also bought here, years ago.
Pre-drilled holes is a plus, or a pilot hole I can punch out for a lens.
I make my boards from model airplane plywood from the hobby shop. I paint them black on the inside. It’s very easy to do using a very few hand tools. And yes, the boards are the same as the anniversary Speed.
For flat boards the ones from the older Calumet CC400 series and even Beseler 4x5 enlarger lensboards will work also. OTOH only the Graphic View recessed lensboard will work.