The aftermarket stuff is junk. Are you using the stock radiator, fan, and clutch? NOTHING will cool your engine as efficiently as the factory setup, assuming everything is correctly assembled and operating properly, including the stock shroud. You can get extra cooling margin if you need it by upgrading from a 2-core to a 3-core radiator or from a 3-core to a 4-core. I see cars every weekend at shows with no shrouds and weird electric or flex-fans, and all of them have "cooling problems", because the carefully-engineered factory "system" has been butchered or trashed because "it doesn't look cool". These are the guys that keep Red-Line "Water-Wetter" flying off the speed shop shelves, and it doesn't work either (more "snake oil"). What WORKS is a properly-sized free-flowing radiator (not an old one full of corrosion and scale) that's sealed to the radiator support, the correct shroud that's sealed to the radiator, the correct fan for the shroud, the correct fan clutch that locates the fan blades exactly half in and half out of the shroud, and a 50-50 mix of anti-freeze and water that gets changed every two years. There aren't any "band-aids" to overcome a lousy cooling system; only two things really matter - an effective heat transfer device (the radiator), and plenty of airflow through it (not around it).
Don't mean to rant, but I see this every summer; pretty soon this forum will be full of "overheating" posts as the weather warms up, and 99% of those problems would never arise if people would just make sure the original factory system is in good shape instead of trashing the pieces and buying all the "cool-looking stuff" from Summit. Unless your car is an all-out race machine, it doesn't need special aftermarket cooling system parts. But, nobody listens - they'd rather have their ride "look cool" instead of having it "run cool".
Simple formula, but the people who mess with it because "it isn't cool" wind up with an engine that isn't cool either.
'69 Z28 Fathom Green