HERE is a link to Oscar's website, showing the absolute best way to do this.
You CAN put the dustwashers below the entire panel, but it leaves a really deep hole that way.
Most of the classic games had the CPO reverse printed on Lexan, and applied to a metal cover plate (Tron, most Williams games, etc...), or they were directly screenprinted onto the cover plate (Gorf, Zaxxon, etc...).
That let them put the dust washer between the top piece of metal, and the underlay of 3/4" plywood.
This kept it right up near the top, where it should be for the best finished look.
An alternate method to the one used by Oscar is to rout a recess around the joystick hole for a piece of metal or plex, put the dustwasher below that, and hold the cover plate in place with glue.
Once you have the plate secured, you can fill any gaps around the edge with a little wood filler, and sand them smooth.
I haven't actually gotten around to finishing any of mine like this yet, or I'd post pictures for you.
(Playable games, and additional controls, keep getting in the way).