I apologize that I missed this message, but just saw it when Paul replied below. In the future, if you need to reach me directly use brouse"at"gmail.com.
NO, do not use a metal shackle.
Place a bowline with a small loop at the swivel end of the halyard. Make the bowline so that the "tail" is inside rather than outside the knot. This will keep the tail from interfering with anything. Now, with the bowline loop about 3-4" from the bottom of the swivel secure with a bowline to the loop a piece of 1/4" (8mm) kevlar, passing the kevlar through the loop and the hole in the swivel 3 times before securing the end of the kevlar. I usually use a stack of hitches to secure the kevlar with the last hitch going through the middle of the line loops rather than around all of them, When the halyard is tight this last pass through the middle gets pinched really tight.
720 Winnie St
Galveston Island, TX 77550