Nikon SB 800 Speedlight extras
Nikon Service in El Segundo, Calif just answered my question. The only difference between these two versions of battery packs is the plug. As the other poster mentioned, the model SD-8A has rounded plug ends which fit the SB800 flash. The SD-8 is identical in all specifications except for having square ends on the plug.
The battery pack I received has the rounded plug. So that saves me $180. Thank you camera gods.
By the way, the service rep from Nikon informed me that when the battery pack is plugged in (6 batteries) it works together with the 5 onboard batteries in the SB800, giving it the juice of 11 AA batteries. Nice to know.