I wouldn’t use the spin halyard for the
jib on my boat for the following reasons. Chafe: The
spinnaker block is above the headstay which it will chafe against if used as a
jib halyard, you also run the risk of getting a cotter pin for the headstay impaled in the halyard and jamming it. The other big risk is, in normal operation, the headstay stabilizes the upper
furling car so the sail can be furled. Often, riggers install
line restrainers on the mast to make the proper fairlead to the upper car. Using the spin halyard will tend to rotate the car out of alignment with the tack which opens the possibility of jamming the
furling gear (next to overrides, this is the most common cause of
furler jams). Another concern is
spinnaker blocks are not designed to carry the loads required of a headsail. Breaking the sheave wheel on that block could jam the halyard. If it was my boat, I’d buy a and thread a replacement halyard. And if I couldn’t afford that, I would re-reeve the
spinnaker halyard as a proper jib halyard. If the jib halyard is completely missing, I’d go up on the main halyard to do this
repair. Or, you can motor your boat over to your new marina.