"One question remains, though. Records show him in Co E, but the marker someone put on his grave says Co B"
Realize that these records were recorded from original handwritten documents some 30 or more years later, some quite faded, ink smudged, holes where folds existed in the document.
It was therefore quite possible to err in transcribing letters, a 'B' can quite easily be taken for an 'E', or vice versa. We see
these transcriptional errors often.