I check out the website you showed. It shows 2 radiators to fit your C-10 with 327. Both say they can be used with automatic or manual transmissions. Not sure why the difference in sizes. Do you not have the original to measure up? Usually 3 cores are considered to be heavy duty, good for towing, AC, ect.... Most radiators anymore come with fittings for various combinations of things and you remove the plugs that you need for your situation. Maybe another Bolter can enlighten us further.