i had the same problem with my z28. descaled the cooling jackets with a mild acid, replaced the waterpump and radiator, went to a dual fan setup from a 350 iroc, replaced the air dam and scoops, and it still ran hot. what i found out was the parts store aluminum radiator had less fpi (fins per inch) than the factory brass radiator, and was there for less efficient. the only thing you can do is either buy a quality aftermarket radiator (griffin, be cool, desert cool), or buy a high cfm fan of over 2,000 cfm. you can also get an oil cooler as well, they can lower coolant temps 10-15 degrees on an older car.