This was hard to find. It was not where we expected to find it when we started looking using the numbers of other graves as reference.
It is on the north side of section 3 (which is sort of split down the middle) up a hill behind Memorial Section D. There is a road at the top of the hill which is closer to the grave, if you're uncomfortable climbing up the hill. Use the map they give at the visitor center, or located at this link
http://www.arlingtoncemetery.org/interactive_map/index.html (link OK on 10 Oct 2002)