The crisscross is installed and works a treat.
The inter board is the vise backer and the outer board is the chop. I've marked where the vise screw hole needs to be drilled on the backer board. The vise needs to be disassembled to drill the screw hole and install the nut. The backer board also needs a top and bottom stub tenon cut along with cutting the left edge at an angle so the backer board fits against the base assembly.
After finishing the vise unit the slab needs to be installed on the base so the vise backer board mortises can be marked. After marking the mortises the whole thing needs to be taken apart to chop the vise backer board mortises. Once the mortises are chopped everything goes back together and the basic bench is finished.
I will make a tool tray for the bench and I expect a full length tool holder for the back edge of the slab.
The fat lady ain't singing but this ol' horse can smell the barn.