I just purchased a used 339 P-90 Pro from the Guitar Center in Houston. It is in almost new condition but with one oddity. The lower tone / volume set is for the neck pickup and the upper set is for the bridge pickup. The selector switch works the same way: down is for neck and up is for...
You might want to ask the question of Gibson Customer Service as to what the stock caps are.
I have gotten reasonable response times from them. What are you trying to accomplish with the change?