This episode contains two historical inaccuracies regarding the Battle of Gettysburg. The actual battle took place July 1-3, 1863, yet the people involved with re-enacting it are doing so in the middle of winter. Admittedly Harry/Jeb mentions that they are re-enacting their own re-enactment so this could be a possible explanation for the date change. The second error takes place when Ray mentions that the actor playing Stonewall Jackson is wearing a beeper. Stonewall Jackson was not at the Battle of Gettysburg. He couldn't have been - Jackson died in Guinea Station, Virginia, on May 10, 1863 (almost two months before the Battle of Gettysburg) after having been accidentally shot by his own men eight days earlier.
The tune Robert is whistling while leaving the basement is, "When Johnny Comes Marching Home", a Civil War related song.