CAN'T FIND 1970 DART 340 HEATER CORE AND EVAPORATOR

Hey, @Road Grabber, have you tried Classic Auto Air? I put one of their "Perfect Fit" aftermarket units in my 69 Barracuda. It works great. They also sell OEM parts and offer OEM AC services. Check them out. I don't know what services or parts they do provide, but it should be worth a call.
Original Air Group | The Factory A/C Experts