Roughly 1000 feet due east from the parking lot at Devil's Den (towards Little Round Top) would have been close to where your ancestor likely died. A couple years or so ago, the Park cleared the woods here to restore the area to the way it appeared during the time of the battle, so it is now possible after many decades to visualize the 48th's position as it emerged from those woods into the ground known as the Valley of Death. Some immediate post-battle photographs were taken of this area and can be found in Frassanito's books. Some Confederate dead that had yet to be buried could still be seen in this location - it is even possible that one of them was your ancestor.