Kreg pads are on the center PC board.
The lack of adjustment of the 6C45P plate voltages is what I would suggest going after. This kind of thing can happen from missing jumpers on the center PC board, possibly from the pots being damaged from being uninstalled (you can put them in backwards, no issue there!). There's an OA and OB on the center board that provide the bias voltage to the 6C45P and allow for fine tuning of the plate voltage. If you turn each of the plue pots ten turns CCW, then measure OA/OB, what do you see? Now turn both pots CW ten turns and remeasure those test points. I would suspect those voltages won't change, and that will help to focus your efforts a bit.