Instead of chain (which does not flex in all directions), I used a series (5-6) oval lead sinkers on some heavy whipping twine which is then stitched to my messenger.
It may be a different inner mast arrangement than mine, but when using the weighted messenger to drop in a new halyard, I made sure ALL other lines inside the mast where tight, heeled the boat over to the side where the halyard would exit before dropping the lead weights. This ensured that the new halyard does not end up wrapping around an existing halyards. I have had that problem, and the friction can get very high.
Chris