This post from @WillAdams links to wasteboard diagrams hosted on C3D’s website for the other machines. I have verified that it accurately reflects the measurements of my XXL.
I intend (and thus recommend) to drill mill the holes in my aluminum board, then thread mill the holes, so that the grid pattern aligns with my machine’s. There will be unreachable areas outside the machining area, but these will purely be for clamping and thus, the alignment will not be as critical for my purposes, and I will be happy to hand drill and tap these (or do it on another machine).