Robert Bohrn knows a little about the two men behind the bronze busts in his foyer. One thing he’s sure of is that this year’s Civil War sesquicentennial adds to their historical worth. He knows they served in the Union’s all black 55th Massachusetts Volunteer Infantry Regiment. That they built roads and fortifications, often under Confederate fire, in Folly Beach, S.C., from 1863-1864 and that they died from typhoid, dysentery and other ailments common in military encampments then. Bohrn, a 54-year-old Charleston, S.C.-born hunter of Civil War relics who now lives in Franklin County, helped unearth 19 skeletons of the men in the 55th.