The Missouri in the Civil War Message Board

Civil War great grandfather

My great grandfather, Jacob Simon (s) served in the Civl War with "The Fourth Regiment Provisional Enrolled Militia Infantry" from 1863 to 1865 (Missouri). Does anyone have info/photos about this unit. Jacob is buried in MO. I have a photo of his grave but nothing on marker indicates her was a soldier. I have copies of military records though, so proof he did serve. He was born in 1842 in VA, died in 1892 in MO.
Another ancestor, my great grandfather, Lewis Piper, also served in the Civil War.
Jacob Sargent was married to Jacob Simon's sister. He also served in the Civil War and perhaps the same unit as Jacob Simon.