66 Dart Gt Idling issues/electrical

Explain the backfire a little more. Is it through the exhaust or out through the carb? Did this engine sit for a while not running? First suggestion after new ignition components, (cap, rotor, plugs, wires,) would be to run through the valve adjustment.
Oh brother. I'm new to the internal workings of the motor. But I just self tought myself how to properly perform a compression test and wet test, after that a leakdown test. I will make a compression tester tomorrow. But for the leakdown I'll just connect with 30 psi. The backfire is exhaust btw.