My 1972 Duster is running VERY HOT!!

Hello all it's been awhile. I took my Duster out yesterday for drive and noted immediately it was running very HOT. Initial indications were a stuck thermostat. I replaced it. Let the car run for about 10 minutes in the garage and the temp got over 200. I noted water flowing in the radiator so I assume the thermostat is working.

When I shut the car down I could hear water boiling in the engine. Any ideas much appreciated.

PS - The clutch fan is working.