The filter drawer for the DII holds two 6" filters. The hole is 5" in diameter. A cut down filter might slide to one side and admit a little white light from the side. Putting some heavy tape, ie: gaffers tape, on the side would build the filters back up to 6" on a side and center the filter over the hole.
The filters should be between the light source and the negative, not in front of the lens.