Engine misfire or loading up when opening the 4 barrel.

Check all the grounds . The ignition box, engine to body ground, Voltage regulator, battery to body, Distributor pickup , also check the air gap on the reluctor wheel. . Did you swapped the carb with one you know works?
I have the ignition box on the fender and the voltage regulator on the firewall. But I don’t have dedicated grounds off the bolts. Yes the carb is a good one