I already have a pair of 2 1/4 X 3 1/4 Graphics (Crown and Century).
My spare Graflok back is off of a Century Graphic.
You wrote: "I b'lieve that the 2x3 Busches with Grafloks that I've seen on eBay had the Grafloks attached to a thin panel that attached to the cameras' bodies."
My disassembly of the Busch Pressman C back revealed a thin metal panel attached to the camera's body with 4 screws (the Busch bellows is attached to this metal panel).
My 2 1/4 X 3 1/4 Graflock backs are also attached by 4 screws - different hole locations than the holes in the Busch metal panel, but same size screw holes. The Graflock dimensions are the same as the Busch metal panel and the alignment is good.
It looks like all I will need to do is drill 4 holes in the Graflok to match the hole pattern in the Busch.