Bryan,
My gt. gt. grandfather was William Harrison Parker of Boone (Carroll County during the Civil War), Arkansas. There was a W. H. Parker in Company E. I obtained his papers from the Arkansas History Commission, but nothing therein indicates that he was from the upper Crooked Creek Valley. The question is, "why would he go all the way to Pocahontas to enlist in the 38th, when all of his younger siblings had enlisted in the 27th Arkansas?" I think I know the answer. Anyway, you say that Company E had some Missourians, so it would not be unreasonable for someone from what is now the Harrison area to have enlisted in a company organized at Pocahontas?
Carl