Snap Shackle
The above is exactly what we use. Be warned that if you use a rope loop in one of these and the tide is running the loop can get caught on the end of the shackle.
End result is you have to cut the rope loop to let the lazy shot (trapeze bar) drift with the tide
Its better to use a large SS ring in the shackle then with a twist it will usually come off no matter what the tide is like.
ATB
Mark