I think you are doing ok on identification of the wires, but there are some troubling things about the setup.

Are the wires in a protective sheath or conduit? I don't see either in the picture.

If sheathed, is there a cable clamp where it enters the box?

Is the wire aluminum or tinned copper? Looking at the clipped ends I think they are Al, which requires special care in termination. The purple wire nuts are also a clue. I haven't used them but recall discussion of special protective grease and purple wire nuts for aluminum. Some receptacles may not be rated for aluminum.

I don't see any clamps, but is this conduit? The caps are blue in person does that make a difference? I believe the wires are aluminum, the color is consistent throughout... The outlet package says it may be used with copper, copper-clad, or aluminum.

That looks like the hind end of a clamp, but you need to see the other side.

Generally conduit is only used where local codes require it; Chicago and its suburbs are a prime example. If you are in one of those areas, it should be pretty obvious looking at your service panel as conduit should be the only thing coming out of it. If it is metal conduit, that's a good thing because the body of the conduit functions as the equipment ground. So you can hook up your new range with the proper 4-wire circuit.

Not so sure what those bits of wire are but it sure looks like someone hooked up something incorrectly. Using 12 or 14 ga. wire on a 50 amp circuit is very dangerous. It's also a clue to shoddy workmanship and other potentially dangerous problems so it might not be a bad idea to get a licensed electrician to give things the once over.