I had a closer look at these packages and they are actually different. Not only the liveries are different, but they also contain different sub-version (read: production versions). The package at simshack contains the F6 photo reconnaissance version, which is not present in package from PCAviator.
Differences are mainly found in the VC, but there are also quite some external differences like the dorsal fin, birdcage vs Malcolm cockpit, antennas, ets.
It seems one is considered the P51B package and the othe is the P51C package
Cheers,
Huub
https://i.imgur.com/ZwcFyZU.jpg