Classic/Antique Car Repair: Radiator question..., thick core, david gardner

Question
Mr. Sears:
I've got a 1979 El Camino (350 engine) with air conditioning.  (Not sure how "classic" it is, but maybe you can help me anyway.)
I need to replace the radiator, and whenever I go to an online parts supplier (hoping to find a good used one), I'm asked to choose between a two inch thick radiator and a one & five-eighths inch thick radiator.  I don't know which I need, and I wondered if there was anything in the VIN number that might tell me?
Any suggestions/advice greatly appreciated.
Warm regards,
David Gardner
davidg32@yahoo.com

Answer
David, I am not a fan of used radiators. We cannot see inside the radiator to check for the buildup of deposits on the tubes. It is the deposits that slow down the transfer of heat from the coolant to the tubes that will cause overheating. With that said if you must use a used radiator put in the best you can find and the 2 inch thick core will remove more heat than the thinner core. This could give you a margin for error. Also I would be willing to bet that with air and a 350 that the factory unit was the 2 inch.
Brad