I have an 04 GTO and I wanted my valve covers powdercoated black. I didnt realize until they arrived today that I was sold valve covers that appear to be from a 5.3 (GM 12561823 CAV 17). I could be wrong, but that is what came up when I googled it.

My question, what exactly do I need to buy since my stock covers do not have the open hole shown in the picture. This is of course the driver side cover and the open hole is in the very back when installed. Mine has a metal nipple as shown in the second picture with the black rubber cover on it. Im assuming I can just buy something to seal that off?