It is possible to over cool an engine, not likely an issue on a street Datsun, on a standard 1200 once you get over 4000 RPM's with the 2 core rad it's going to run on the warm side. A 120Y rad will do the job (that's what we did) for a road car.............for our 1200 GX powered track car I run the GX 3 core radiator............rev it to 8K all day and it's often 100+ degrees out. (it does get warm in Vegas )

Tom