I didn’t see any posts from anyone else about this so here was what I’ve done (so far).
I 3d printed the Corner & Center pieces from the Not Shop and used them as a template on my router table with a flush trim bit. As a bonus I have the screw holes all uniform across all of my parts.
I plan to use the 3d printed anchors that @Dan_Bunby designed but I did use a 9mm drill but to mark the center of the anchor holes if I decide to go that route later.
Corner Block https://photos.google.com/photo/AF1QipPZuU2odal64xZhPjz38XH6ZP8bQAKTokxvXsUZ
https://photos.google.com/photo/AF1QipMKUd-x8hPpWDvx5_gvbJxTy3rqL-DLAEtapEFZ
https://photos.google.com/photo/AF1QipODuwXPfzpEa911RcPAUxc15K2TXPYQLWddwpHd
Inner Block
Unfortunately Mother’s Day weekend got in the way and the rest of my build is on hold for the next couple of weeks.