Finding a new heater core.

So winter is coming and its time to get some heat in the car. I have a 63 dart non ac and im looking for a new heater core and heater box gasket kit and while im under there might as well get new wiper pivot seals. My problem is the heater core and pivot seals. I can only find heater cores for a 65 dart and a 63 and 64 valiant would either one of those work and there are two types of pivot seals, ones with square white gaskets and one with diamond shaped white gasket and i dont know which to get. Thanks for the help.