What are your voltage readings after installing the Speedball?
Those white resistors will be about as hot as they were without the Speedball, and I would expect them to be between 150 and 200 degrees Fahrenheit. Also, when the amp is running, the highest voltages in the circuit are around these 270 Ohm resistors, so if you're touching them while the amplifier is running or very shortly after it has turned off, then you are bound to shock yourself eventually. Also, the voltage measurements given in the manual will actually tell us if those resistors are running too hot.
The crackling that you describe is a broken wire or a bad solder joint, and you have that reasonably well narrowed down based on where it's happening in the amplifier.
-PB