push button swap to b&m auto shifter?

The easiest way to tell if its a "push botton" transmission is to look at your front driveshaft yoke where it mates to the back of the trans. All late style 904's (non push button) used the slip yoke design. All the early "push button" tranny's used a (4) bolt flange to attach the ball and trunion u joint to it. Unlike 727's there was no transition year with a push button front half and a later style slip yoke back half. There are other differences also, but I highlighted this one because I thought it would be the easiest for you to identify given that I don't know your level of familiarity with mopars, tranny's and automotive in general. If the terms like slip yoke or ball and trunion aren't familiar you can get clear pics of each from a web search to compare to what you have. If you are unfortunate enough to have the "push button" trans in this vehicle and you wanted to go back to the correct late style trans you would also have to change/modify the driveshaft for the reasons mentioned above.