Yes!! you are a rocket man! Thank you for correcting me on the size of the Riv fan you are correct the 1972 Riv is equipped with a 18" 7 blade fan as you stated. So good question where did this 20" 7 blade come from? I think keeping everything GM is the correct way to go. The brass/copper radiator I pulled out was a modine 3 row. Going to bring it in and have it serviced. I replaced the thermostatic fan clutch but I will check it out anyway.
No No No a Riviera did not come with a 18” 7 blade fan. Where are you getting that from???? It’ doesn’t fit the fan shroud which is bigger in 71-72.
Incorrect information causes people to make restoration mistakes when they read these threads which is a huge issue as correct parts gets tossed. Use what you want on your car obviously but try and keep what is correct obvious.