Well, after many months, I have finally gotten around to finishing my Crystal Castles control panel. I first sanded most of it to remove rust then gave several coats of Tremclad Rust paint (satin black) with curing done in the sun.
Today I applied the (repro) overlay from Arcade Renovations and discovered that it has a similar problem to the marquee/speaker overlays. It's common knowledge that these overlays are not as opaque as the originals, and for the marquee, light shines through the blacks making it look a bit greyish.
A similar problem exists for the CP overlay, but for whites. When glued down, the whites show a bit of the black underneath (apparent as slight, blotchy grey). You can get rid of this by rubbing those spots repeatedly, with your finger nails until you're left with a uniform color (but it won't be a pure white like the original panel art should have).
In the end, the difference is negligible, but noticable if closely inspected. If I were to do it again, I would paint the panel white first, and only paint black where it really needs to be black.
Overall though, the machine looks brand new now.
~Ray B.