In my -4, I have a dynafocal mount and used a B&C Specialty Products right-angle filter adapter and spacer. The spacer is either 2.5" or 3" and clears the mount by 1/2" to 1". Clearance has proven to be sufficient. I will look to see if I recorded the actual spacer size and will update the posting if more info is available.
Good luck,
Dean Pichon