1972 Chevy Camaro Running hot

I have a 1972 Camaro with a 455 Buick engine and 400 turbo trans. I used this engine a few years back in a 1968 Camaro and in cooled ok. We always had the car running at racetrack and operated at 195 degrees. But now in this other car it gets up to 210-215 degrees at stop lights. The engine is newly rebuilt, new water pump, 3 row radiator ( had cleaned before install), fan shroud with 17 inch flex fan. It has a 185 degree thermostat in it. I just installed two electric fans in front of radiator but it didn't help. My questions are :
What is the proper spacing of fan to radiator?
What type of fan is better, flex or stock?
Is the thermostat correct?
Do I need a bigger radiator or aluminum maybe?
Please help, thanks Bobby Howard