69 Dart cooling questions

It is all about the surface area as stated. Do you know how thick the cores are? I bought one from wizzardcooling.com out of new york and so far I cant get the car over 155 degrees idling in the garage for an hour. I have a high flow 160 t-stat and high flow 8 blade water pump. Here is a pix of it. Looks and functions great. By the way my cores are 11/4 inch thick x 2

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