440 getting hot

Hey guys,

Need some advice just rebuilt a 440 getting hot after 5 to 10 minutes of start up idling good purple cam AA heads dual carbs. what i v done re-core rad. new thermostat, taken heads to get checked out manga flex ext. took heads off 2 times just to make sure i installed them right. ok looks like top end heads maybe i think exhaust getting through the water some ware. please any info would really help.