OK Folks.
1. A rb67 Professional rig shoots a 5.6 x 6.8 negative.
2. A rb67 pro body + rb67 pro rotating adaptor + 6x8 power back gives a 5.6 x 7.2 negative.
3. A rb67 pro body + rb67 pro-sd rotating adaptor + 6x8 power back gives a 5.6 x 7.3 negative
And, John, you were correct . . . the pin unscrewed