I'm with
rccardr , shorten the existing FD. Another possibility would be to cut both ends of the cage off and use a screw or a screw and a bushing to act as the new bottom stop. Some of the older C&V FD were made this way. Use Loctite to secure the threads. If longer space is needed on the inside cage fill the elongated cutout with epoxy first. Let cure, sand and shape.