This list (a 6.06mb pdf file) has had the three surviving MkVIIIs listed for some time, but has not been able to show a picture of this particular survivor. For a while, it wasn't clear if it was the same tank at Fort Meade and APG, or two different ones.
I was at APG in 2009 and 2010 and there was no MarkVIII there. Just the MKIV and a Whippet. I tried to get into Fort Meade to see the advertised MkVIII but the line up to get a pass to enter the Fort was long and one guy working at the desk. What happened to the skeleton tank at APG? Its disappeared.