overheating problem on a 73 455

[skylark455th350]

i have a 72 skylark with a 73 riviera 455 rebuilt top to bottom honed and cleaned with full rebuild kit. i have a three core radiator that i picked up at a local parts store with a flex fan that pushes good air. Also an electric fan on the front of the radiator for a little extra cooling power. I have tried running a little rich and tried different thermostats a 180 and a 195 but still when i am at idle between 650 and 800rpms i cant keep it cool and the engine heats up quick even when it is around 70 outside. I was wondering if anyone had any idea how i could cool it down i really don't wont to fork out the $400 to $500 for a 4 core radiator does anyone sell a performance water pump or any other ideas will be great fully appreciated.