A picture of the logic-board end of the ribbon cable would be a good start. Accurate dimensions of the actual keyboard plate as well.
I'll fess up - this is a crazyplan to replace the awful keyboard in the Powerbook Duo. Everymac tells me the case dimensions of the 12" iceBook and G4 Powerbook are a match, near enough. Yes, I know case surgery will be involved, even if they fit at all, and various other hacks and kludges - this is not a showstopper. And various sources tell me that the Powerbook keyboards used ADB up into the G4 era: I'm not sure exactly when the changeover happened to USB, so the earlier the model the better, just to be on the safe side.