It looks like you have a super radiator. Also I agree with comments that hot at idle and cool when running usually indicates lack of air flow.

Most aftermarket electric fans are sold and intended for supplemental air flow only - they don't move enough air to be the primary cooling source. There are some well engineered OE setups on newer cars... mostly mild 4 cyl or V6. Higher power setups - Durango's, Pickups, Jeeps - still use an engine driven fan. If you found a really big aftermarket fan it would cost several hundred dollars and suck your stock style alternator and battery dry at idle. You would be into a couple hundred dollars more to upgrade the charging system.

The thermal clutch fan worked well on these cars originally and still does. Here's a setup that has worked well for me on a 496 B with AC.

Radiator: High capacity aluminum
Fan: MP 5 blade thermal clutch fan
Shroud
Water Pump: MP high volume, slightly overdriven (6.25" drive pulley, about 5" fan puley)
Thermostat: 180 high flow Mr Gasket


With extended idling in hot weather and AC running it gets up to 185 or 190. I had a higher capacity 7 blade fan as backup when I hooked up the AC but didn't need it.