I had the same problem with my engine (428 as well). Did pretty much everything Rick recommends, Edelbrock pump, 1:1 pulleys (got mine from Kirkham, gorgeous billet), 180 thermostat, 50/50 mix. But the big improvement was a radiator shroud. I have twin 11" fans and had an HVAC shop make the shroud for me, cost was $120 and well worth it. No overheating now.
As it turns out, I have a slightly used Edelbrock water pump I want to sell. It came off a 428 a fellow here built and it ate the cam in 16 miles. He learned the lesson of proper flat tappet cam break-in. That's all the miles on the pump. I'll sell it for $120, plus shipping. Part number is 8805 and it sells for $190 new at Summit. Email me for pictures if you are interested.
santafe66@excite.com