How to attach asym spin head to top down furler?

[Whomda]

I am trying to attach my asym spinnaker to my top down furler using an anti-torsion line. The tack is attached as clearly described in the furler information guide.

The head, however: The anti-torsion line fits neatly into the furling swivel, but how do you then attach the top of the sail itself?

I have hooked it on using a shackle (see pics), but this seems like it might create a lot of stress on the sail.

What's the intended way to do this?

[gabilo]

Remove the steel ring and add a dyneema loop. Or instead of a steel schuckle use a soft shackle