Factory 440 Darts had 22" brass radiators with 3 cores of 1/2" tubes, most other Mopar radiators used 3/8" tubes. Aluminum radiators do not cool as well, so the 3 core with the largest tubes you can get would be the best.
How do you figure? 3 x 1/2" = 1.5" of cooling tubes. 2 x 1 1/4" tubes = 2.25" or 40% more volume and surface area for the air to pass over and cool the fluids.
