1. Bert's got 20 years on me.
2. A standard film holder backing plate is .197 ± .007 from the film holder edge for formats 2x3 through 4x5. http://home.earthlink.net/~eahoo/page8/filmhold.html
3. A Graflex film holder backing plate is .224 from the film holder edge in 4x5, tolerance unknown.
4. The view hood ground glass can be shimmed up to 1/8 inch (.125) higher without causing problems, lowering more than .010 inch may require milling the mount opening down.
5. TriX TXP sheet film is .007 inch thick.
What is the delta difference between the base of the Gralex mount and the Graflok mount to the same point within the camera body? The math states you have 0.015 to 0.150 to play with, yes?