You can do fibre in a big quad but it can be tricky. The fibre holder probably won't be of any use as it needs a slanting slot to work but you could try it, I suspect the paper will just buckle though. I've heard that many folks use two clips to hold 12x16 inch fibre paper and gently move from slot to slot in a quad.
You can probably adapt the fibre holder to work in the original Nova slot processor. I was the photographer who persuaded Nova to make a fibre clip and worked with them for over 2 years in helping to design and test it. The original idea was to make a clip that would work in the upright processor but we did have problems in stopping the paper from slumping downwards and came up with the idea of the angled processor. We did have a clip that worked with fibre paper in the upright processor but it was quite a fiddle to load the paper on to it and it also involved fixing the paper along each side with a clamping device.
I have made 12 x 16 fibre prints in the upright slot processor using one ot the original clips and supporting the paper along the bottom with the tube that lies in the top of the slot as it is transferred. I found this more efficient than using two clips.