'64 Dart questions

Hello and welcome!! I also have a 64 dart 340 but with a manual 4 speed 8 3/4 rear with 391 gear. You didn't say as to wether or not you have the 904 or the 727.I have enjoyed the push button trans with the / 6 in one of my old darts.You can tell if the trans is a 727 if you look down the trans filler tube and at the point to where the tube goes into the trans has a kickout to where the 904 is just squared off at that particular corner.I beleive the the newer 360 magnum engine as well as the older style la series engine would interchange with no adapters.As for the stronger rear end the 8 3/4 would be best but $$$$$$. If you are on a budget you could try an 8 1/4 rear Identified by the center of the rear end being rounded at the top and bottom but squared on the left and right sides.The 7 1/4 is rounded all the way I believe.BUT BE SURE THAT WHATEVER REAR YOU GET THAT ITS FOR AN A BODY!!!I hope all the info is correct and helps!