I'm not really a morph-guessing person, but I do find this pretty interesting. Pewter's one of those that has extreme amounts of variation, even though it's only two morphs at play.
Here's a pic from WOBP of two pewters that look pretty similar to yours:
https://ball-pythons.net/forums/cach...pewter/008.jpg
On the other hand, as StillBP pointed out, it also sort of looks like a pastel RA. They have a lot less variation than pewters, and are more likely to have the lighter back strip and head, and close keyhole markings, like this one from Freedom Breeder's website:
https://freedom-wpengine.netdna-ssl....-4-600x600.jpg
Honestly, the side pattern does remind me of my own red axanthic (which does happen to be one of StillBP's creations lol). You can see the lighter pattern on her spine and head is still pretty obvious, even though pastel isn't present. And I stare at those keyholes/alien heads/whatever you call them often enough that I can see a little bit of similarity between them.
Like I said, though, I honestly have no clue. He's a pretty little mystery!