Your explanation was good. If you get popping sounds from the exhaust and the carbs, it means one plug is firing on the exhaust stroke, and another plug is firing on the intake stroke. That means they are firing out of order, and most likely the plug wires are swapped. I found this out rebuilding an old land rover, with no markings on the distributer to tell me which wire belongs to which plug. I actually had flames firing out the top of the carb!
Glad I could help.
Happy and safe travels.
If its stupid, but it works, it aint stupid.