Since FP100C is 3.25x4.25, I've been thinking about how I could adapt a polaroid back on a 3.25x4.25 Speed Graphic. Perhaps something like a series D.

And then I thought about my Hasselblad polaroid back. Could I theoretically take the 6x6 mask out of a Hasselblad back therefore exposing the whole frame?

Would it fit on a Speed Graphic, or could you somehow adapt the back of the SG to accept the polaroid back?