Back Firing, Surging, and Bad Noises from Engine

[72rookie]

The old C-10 (Bessy) has started acting up. The engine has started back firing through the carburator, and surging, and sounds like hammer going off inside of the engine. This has all started happening in the last week and a half. Our initial thoughts were that the timing was jumping due to a possible cracked distributor cap. Last night we replaced the distributor cap, rotor, and plug wires and unfortunatly no change happened with the motor. I need your guys help to help diagnose the problem and put my worst fears to rest. Please help.

Thanks,
72rookie