anyone wired in a retrofit radio for a 67-69 Barracuda?

Keep in mind you'll need a wire that has +12 on it at all times in modern radios so it doesn't "forget" settings. You'll still need the switched +12V too. Unlike the factory units, 'most any car radio made in the last 35 years or so has "floating" speaker outputs, ie-don't ground them or you'll damage the receiver.