Replace heater core?

Coming home from CarCraft today (St Paul, MN) in 64 Valiant when suddenly my heater core decides to a crap out and start leaking out my passenger vent door. I've switched heater core and fan motor in a 68 Dart, how much different is a 64 Valiant? Any tech articles out there that would help me? I don't have a service manual for 64 but do have one for 68 Dodge Dart. check back later, Mark