Factory Radio Wiring

If you find an old speaker yes. If you get a regular generic 8 ohm speaker then the green goes to + and the black to - on the speaker leads.
You can find the male/female connectors at any store, even auto parts stores and make your own connectors.
Remember these were mono radios back then. You could fake 'stereo'
by using a 'reverb' unit with a second speaker and you would install that in the back. The tech manual for the 66 Barracuda has pictures for that.