Shelby Stanton's Vietnam Order of Battle may have some info. I'm in the process of moving and my copy is packed away somewhere, otherwise I'd look it up for you.

I was told the Sharpshooter is from the 20s

Hello Fellow Members,   Are these WWII bullion pilots wings English or US made?  The backing material appears to be the standard US Army officer tunic material.   Many Thanks! Dave.

Anyways to actually contribute to the topic, I believe the sixth ID painted the 6 sided star on helmet going into the Meuse Argon, I may be wrong, but I feel like I have seen photos or read something about that in a period unit paper or something of the sort.

Oh my, it’s been a Long day, That is not true, disregard what I said, I was thinking ww2! Sorry for that! 

Note the subject is "pre armistice division/unit marked helmets, " so that's WW1. The WW1 9th Division was formed late in the war and did not go overseas.

Another thought. If you have a vise stout enough to hold your receiver section, a large pipe wrench will likely crank that barrel on, though the surface will definitely get chewed up where the wrench bites or slips.   The Marines barreled M1903 Springfield rifles using plumbers pipe vises. Those will also leave a mark.

I thought the 9th Id were stateside when the war ended and never deployed?

I've used Oak pallet scraps and powdered rosin clamped in my vise or to my workbench as a barrel vise in a pinch (though not on an M1 though the process would be the same). The advantage of the M1/M14 chamber profile is that with the two different radii where the barrel tapers down in front of the chamber is that they pretty much can't spin in a properly set up set of vise blocks short of the blocks failing.  

9th ID MPs had divisional octofoil markings on helmets