I can't figure out where this rectangular hole is located, however, it appears to be near the hood hinge. Could you please post a picture that isn't a close up of the hole?
I have no idea what the second picture is of. It looks like it is near the floor, but that is all that I can tell. If it is a light, I would need to see it at a different angle to figure this out.
Third picture......
To change the lenses, you have to use a small tool, such as a very narrow flat bladed screwdriver, and gently pry the lens down. There are either 3 or 4 tabs that hold the lens to the light housing. The bulbs are either a bayonet type that twist to remove, or they might be the long cylindrical type. Both types were used in your vintage car. When you get the bulb out, there is a number printed on the side.