727 or 904 in a Early A body

Hey guys, i'm relatively new and building a car with my dad. We've got a 4 spd setup that was planned to go into our 65 valiant (dart) but now we're kicking around the idea of putting an automatic in it. We have a rebuilt 727 out of a previous project, would this fit in without a lot of work? Or would a 904 fit better? If 904 for fit, what kind of mods would you guys suggest for it to work well behind a 415hp 408cu, not using for the strip, just some aggressive street driving!

Thanks in advance for your help,