273 Overheating problem

I'd start with the basics, test the thermostat. Get an accurate thermometer and check the opening temperature, stick the thermometer in the radiator and watch for the coolant flow in the radiator . If that checks okay, then try changing the fan and installing a shroud. The other consideration is the pump and fan pulley, are they matched to one another ? An AC pump has a SMALLER impeller and pulley than a non AC pump, mix them around with the pulleys and you have inadequate flow.