From the factory for 70 Darts with a small block - the AC cars and the 340 cars came with a 3 core radiator (three layers of flat 'tubes' from the engine to the grille) . 318 cars with no AC came with a 2 core radiator (significantly less cooling capacity) unless you ordered a high capacity cooling system (for example you planned to tow a trailer or a boat, or you lived in a place with steep roads) and then you got the three core. You should be able to look into the filler neck and see what you have.