Engine breaks up at WOT

Have a question. 1983 Z28 with a 350 cammed up, headers, and eldelbrock goodies including a 600 carb. When the motor is cold it runs a pulls great! Once it warms up it runs and idles fine until I put the pedal to the metal it seems to start breaking up at the higher rpms. Popping and sputtering like a fuel or igntion issue. Looking to buy this car so I dont know if I should stay away. No temp gauge on it either so I dont know how hot its running but the owner drives it everyday on the highway and city all summer with no tell tale signs of overheating. Its a nice car. Could it be wrong plugs? Wires new along with cap and rotor, timing set correctly. Leaning out, starving for air? He has some chrome lid, small paper element air filter on the carb. Small, like 6" in diameter, 2" tall element. Any ideas?

Have a question. 1983 Z28 with a 350 cammed up, headers, and eldelbrock goodies including a 600 carb. When the motor is cold it runs a pulls great! Once it warms up it runs and idles fine until I put the pedal to the metal it seems to start breaking up at the higher rpms. Popping and sputtering like a fuel or igntion issue. Looking to buy this car so I dont know if I should stay away. No temp gauge on it either so I dont know how hot its running but the owner drives it everyday on the highway and city all summer with no tell tale signs of overheating. Its a nice car. Could it be wrong plugs? Wires new along with cap and rotor, timing set correctly. Leaning out, starving for air? He has some chrome lid, small paper element air filter on the carb. Small, like 6" in diameter, 2" tall element. Any ideas?

I know this is a necropost, but I am replying because someone else might see this and benefit.

You say the engine is 'cammed up', but my question would be who did it and with what. What was the cam used, are the valvesprings factory? Almost sounds like valve float.