1962 Valiant Signet 200

My understanding is gauge faces are aluminum, is this true?

Yes, each individual gauge face is made of stamped aluminum. The instrument cluster faceplate is plastic.

Are the white knobs just plastic?

Yes. The radio knobs should match them; those chrome ones don't belong.

Horn ring appears to be broken.

'62-'66 Dart-Valiant-Lancer-Barracuda. The full-round horn ring available on fancier '65-'66 Darts fits correctly, too.

My guess is the remote speaker control under the dash is aftermarket.

Correct.