The Power valve Channel Restrictions (PVRC) are a part of tuning a Holley not known by many.
The power valve add's additional fuel above what the main jets can give. It is simple to tune them , but patience is key. Buy a numbered drill set. Find the one that is the same size as your PVRC. For example :to add 10% more PVCR flow. Calculate the area of the size bit you find to match existing hole. Now calculate 10% more area in size and find the corresponding bit. Use a hand operated grip to run the bit in. Now the PVCR will flow 10% more fuel.
Maybe you will want to start with less than 10% change, but you get the idea.
The goal is to run normal sized main jets for fuel economy and let the PV supply the fuel when really getting on it.
What list # is your 390 carb? It may not have PVCR in the rear, infact no power valve. Just a plate or jets?
