Cooling Issue - 1964 Dart GT - 273 with automatic and A/C

Update -

The lower radiator hose was the issue, as it was collapsing as noted by some on this thread. Replaced it with a new one, as well as the thermostat that failed in the open position, and it now cools perfectly. After a half hour of stationary run time in the sun, I can't get it to get over 202 degrees at the temp sender location on the intake manifold, as verified by an infrared thermometer. This is using the 3,000 cfm electric fan with sensor and relay.

Since I need to drain the coolant again to install a spring in the lower hose, I'll likely try reinstalling the mechanical 7-blade fan with a taller spacer that'll get it closer to the radiator, and see how well it cools without the electric fan.

Many thanks to all for your thoughts and help!