Doc I think it may have more to do with quality than cost. The radiator in the 69 that dealt me fits had a brand new core in it. The engine temp would continue to climb at highway speeds after a fresh rebuild. I later found out it had always ran on the warm side.
The heads were pulled and checked a a second reputable shop and reinstalled with no change.
he motor was then pulled again and 3 frereze plugs were found inside the water jackets. AHA!!!!
Reinstall, no Chnage.
Pull motor again and send to second reputable shop. Minor issues but nothing of any consequence.
Reinstall, SOS.
Talk to Glen ray. Send him the radiator. It comes back, install it and temp never goes above 190 even on the hottest days and hasn't to my knowledge 5 years later.
All readings were being taken with a laboratory grade digital meter and thermocouples which are accurate to 1/10th of a degree. You wanted the story, You got it! BTW the above is the short version.
I have had a few other similar situations since then and in all cases the quality of the core being used was the root of the problem