I took the opportunity to change the green cable that joined the metal casing to grounding. I just didn't like it. But this is optional.

Now, fix the PCB to the wooden base plate. Use the original black plastic washer for this while being careful that the PCB itself does not touch the aluminum paper.

Next, reattach the metal casing with its three screws, first one to fix the PCB to the case and then the two to fix the metal case to the wooden base plate. Remember that the black metal box has to touch the aluminum foil.