Mercury arc rectifier

[ppppenguin]

I've got a router so that's probably the answer. I'll clamp the original metal panel to the plastic, the screw holes are ideal for this as they will be needed in the plastic. Then clamp a guide bar suitably inboard. If the router cutter gently touches the metal it shouldn't do much harm to either the cutter or the metal.

There are a couple of rounded corners which I can cut with a fretsaw and sand to final finish. Or dare to rout freehand with the metal panel to stop me going too far.