To keep it simple.
At the beginning you said that you could stop thermo fan by hand when hot.
It is buggered.
Reverse flushing the radiator with garden hose, not very effective. It needs the tanks removed and cores cleaned with rods.
You said, top hose very hot, bottom of radiator cold....it it blocked. sediment falls.
Had exactly same issue with old Jaguar radiator, top hot, bottom cold. I watched the guy at shop do it. Shocked that 1/3 of it was completely
blocked.