I believe Spinlock claims not to damage line. How is the current clutch mounted to the mast? How are the backing nuts held in place? You may find that they drop off when to remove the current clutch. If that is the case it does not matter where the new holes need to go. If the nuts are secure you can build a face plate that mounts in the current holes then mount a new clutch to that.
If space is a problem you could move the exit hole for the halyard further up the mast.
Ever consider a small mast mounted winch. Solves the rope problem and eases the raising of the sail.
Other option is to devise something like a H16 that uses a wire rope combination that hooks in place.