Firewall and cowl interchange question

I have couple questions. I have a 67 Dart GT, the firewall & cowl need work. I was concidering buying a Dart parts car. First question are 67 through 75? the same? Will a 4 door firewall and cowl work? I'm not worried about minor cosmetic differences. The car won't be anything close to stock/original. Will other A-bodies work besides another Dart? Duster, Barracuda, Valiant? Thanks for any help, it's appreciated.