A-Body 440 cooling problem

Depending on how much HP you are making a clutch fan with a shroud using the stock big radiator like you have should cool the beast.

The basics are what you need to look at :

Verify the operating temperature using a mechanical or mercury thermometer. The electric guages are not accurate.

Are you using the correct factory designed pulleys for your engine application ?

Are you using a shroud ?

Are you using the correct water pump for the pulley set up ? This is extremely important. The impellers on AC pumps are smaller and are matched to a smaller water pump/fan pulley, If you feel you need more flow use a NON AC pump with the AC water pump pulley. The impellers on Non ac pumps are larger, and are matched to a larger pump pulley used in non AC applications.

Are you satisfied that your thermostat is working correctly ?

Are you using a coolant water mix ?

Are you running enough initial timing ? Retarded timing will cause excess heat.

If any of these are out whack then you may have issues.