Help with Ross MK II Unit Markings

[Arisaka99]

This one has a lot of history. Expertise appreciated. I picked this up at the Hampton VA show on Sunday. US marked, so part of the 20k purchased in 1917. All the cancelled armorer stamps show quite a bit of use. Can someone decipher for me? 5th Pioneers is easy. All the CEF are training marks from England? Thanks!!

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[Arisaka99]

I am sorry... I forgot to mention. I am a US collector; not a dealer. This is going into my collection and staying there. I am just trying to research so I learn. Thanks again.