What you have is an early Pacemaker Speed Graphic, 1947 to be exact. www.graflex.org > cameras > Graflex Graphic Model History > Pacemaker Speed Graphic = http://www.graflex.org/speed-graphic...d-graphic.html
Rear shutter must be at O, front shutter must be open via the press to focus lever, locked open on B with a locking shutter release cable, or open on the first trip at T to see light from the lens on the ground glass.

User manual: http://www.cameraeccentric.com/html/info/graflex_5.html

Ground glass replacement is an easy task. The ground side always goes toward the lens.

http://www.cameraeccentric.com/html/...raflex_12.html will tell you what you need to know about leaf shutters used on these cameras.