Joe it's too bad the portrait orientation doesn't work with your original Nikon F bellows. It works with the PB-6 because the piece that mounts the rails and would hit the grip is much lower than on yours. To mount the bellows you need to clear the D700 grip. The grip extends about 10mm from the lens mount and the piece that holds the rail extends about 8mm so you need an extension greater than 18mm. You can measure your gear to verify that number but it should be close. Since you don't need a tube with contacts an inexpensive one should be OK.