Steve,
My wife had a gg-grandfather and two gg-uncles in Company E, the "Mount Vernon Guards". Have you seen this info from http://stevegibson0.tripod.com/co_g.htm ?
JOHNSON, James; laborer; age 36; enl. 25/4/61, at Alexandria; Pvt., Co. G. Died 11/9/62, in C. S. Hosp., Petersburg, from effects of gunshot wound just below right shoulder.
Jim Martin