Really all that's needed is sand the top flat (wet sanding is best). Round off the edges and engrave the top if you want or leave it as is - then colour the piece with gold/silver paint/coloured wax/whatever you want to use. Drop the piece PCB assembly in and use a little glue (from the top) to hold it in place. Push in the nixie.
I used hot melt engravers wax for the ready built board pieces but never again - too many burned fingers.
Piece base case
Assembly instructions for the V1 chessboard.