jnanian,
The .010 or so difference in film plane position between standard and Graflex film holders will not have much difference on images shot at small apertures but will on images shot at wide apertures. You may have gotten your taped on holders close to the actual film plane of the camera. TXP (triX 320) in 4x5 sheet is .007 inch thick. T Max in 120 is .0045 inch thick.

http://www.flickr.com/photos/thirteenthumbs the 3A Graflex I made a new shutter curtain and modified the transport to use 120 film; the 3x4 RB Auto I made a new shutter curtain and an adapter to use standard 120 RFH.