Dash Questions

[Longhorn Man]

That hole would be the high beam indicator. Should have a red lens in there. Some had a rectangle hole, but the round one is way more common.
I usually prefer to use spray paint. Chevy orange is a good color IMO, but not anywhere near the red-orange that they are supposed to be.
As for the rust...You are pretty much screwed. There is no way to remove it without harming the paint and the lines, and while you could get the white overlays (could even talk them into making black ones) the rust would bubble up under the overlay in very little time.
If you were to post a guages wanted post in the parts section, I'd imagine you could score some fairly cheap. And if you are lucky, whomever you get teh guages from may know how to set the odometer to the same reading as your original unit.