The Polaroid 405 or Fuji PA-145 are for the smaller pack films. The Polaroid 550 or Fuji PA-45 are for the larger pack films, which only Fuji has been making for a few years (Polaroid stopped these pack films several years ago). The exposed area is 90mm by 122mm or about 3.54" by 4.8". Just for comparison 4x5 transparency film has an exposed area of about 95mm by 121mm.
The naming of some Fuji Instant films and the holders they make do seem to cause slight confusion. When you see FP100C and FP100C
45, that
45 indicates the larger pack film. Both those films are 10 shots in a pack, but they need different holders. The Fuji PA-145 is the smaller holder, and their PA-
45 is their larger holder. The smaller pack films will not fit nor work in the larger holder.
Whether either could be converted for wet plate work depends upon your skill converting them. Considering that used any of these holders are now going for fairly good money, it might be cheaper to modify different holders, or find some old vintage holders instead. Most of the Instant pack film holders I have seen tend to be made mostly of plastic, though many have a metal base.
The Polaroid 405 or Fuji PA-145 might fit under the ground glass spring back of most 4x5 cameras. It would be tougher to do the same with a Polaroid 550 or Fuji PA-45 holder, because these are thicker; you might break the springs on some cameras. All these holders have slots which would work in a Graflock set-up, and I would recommend using them that way.
Ciao!
Gordon Moat Photography