[Baba O'Riley]

I bought this radiator for install in a 1971 Formula 400.

On the old radiator, the radiator's 3/8" cooler lines bolted directly to the fittings on the radiator tank -- with no line fitting or connector. But these fittings on this new radiator don't fit the original lines like the original radiator did. (I've owned this car since 1992 and I'm the second owner; I'm pretty sure these are the original lines.)

The lines on the car fit a 3/8" female brass plumbing coupling fitting, but what is the size of the connection that bolts into an aftermarket radiator? My local auto parts store offers connectors that are 3/8" x 9/16-18 and 3/8" x 1/4-18 -- does either fit this radiator? Or -- is there an AC Delco, Dorman or Quick Disconnect part number for the right one?

Thanks as always.