CAN'T FIND 1970 DART 340 HEATER CORE AND EVAPORATOR

I think they're different, but can be made to work- don't quote me on that!
There's options on EBay. Break out the gold card.
1967-73* DODGE & PLYMOUTH A BODY A/C Evaporator AC Air Conditioning MOPAR | eBay
Heater Core For 73-76 Plymouth Dodge Duster Valiant Dart Scamp XB12Z2 | eBay (Note: '73 and newer version- compare to yours)