There is a locking TAB on the original oil filler on the valve cover. The two parts are completely different from the mount to the cap. You can grab the base with a set of ChannelLocks and a rag, moving it with slight authority until the actual locking detent releases the mount.
I bought a much
longer one from O'reilly Auto for $33 and have not mounted it on my car as I have been working on "Frosty" lately. I raised it up so I can add this
-10AN oil filler cap to pull a second vapor attachment for the Air-Oil-separator and help keep oil from filling the catch cans as most of the tracks have very long right-hand sweeping turns.
See the links. There is a tab you can get to come loose then the CAP will fit perfectly aligned.
Watch this YouTube Short to do it right!