O/D A/T behind a 440??

So hypothetically, if I were to put an overdrive transmission behind my 440,(69 Dart btw) what options do I have? And BESIDES THE CUTTING OF THE TRANS TUNNEL SUPPORT, how hard would this be to make work ie; do they make manual valve bodies or would I have to run a kick down or vacuum or what? Could I use my 3 speed shifter and add a button for od? Like I said, just brainstorming. Any info would be useful! Thanks in advance guys!