[1968 nova ss]

I know the 4 core nova radiator are gloss black in color.Had to remove the rad and have a small leak repaired.My question is;I have a quart of ppg 9300 urethane paint ;will it hold up to the heat of the radiator ;or should i use some high heat paint from a spray can ,by the way ;when flushing out the block and particular ways anybody goes about flushing out the block.thanks,chris