Engine and tranny help

I just bought a 1964 Dodge Dart with a Slant 6 engine and 3 speed TorqueFlight transmission. I'm having some problems figuring things out. First, does this car have a 904 or 727 tranny? How can I tell? Will a 340 bolt to my transmission? Or do I need to get a different transmission for the engine? As you can tell I'm new to the car game but my 13 year old son is MOPAR crazy. Any help is greatly appreciated!