Cooling issues 69 Dart GTS 340

Things I've checked out.
stock 2 core radiator
7 blade fan
fan 2 1/4 inches from back of radiator
crank pulley 5.2 inches dia.
fan pulley 6.5 inches dia.
180 thermostat high performance
I have heater core supply line plugged (heater core leaks)
What else should I check or what do I need to change?

Temp climbs if idling
turn off engine temp climbs