We have something similar to this mounted low on the mast for the halyard>http://mauriprosailing.com/Merchant2/me ... =BIGBULLET
The single swivel cam next to the one for the furler is most likely for the tackline on the spinnaker. All you do is pull the spinnaker tack out to the end of the pole with it.
I have no idea what the other two are for. I wouldn't use them for the spinnaker halyard. They were probably someone's idea of what they needed. We liked to keep lines on deck to a minumum and even rigged up micro blocks up inside the wing tramp lacing so the trapeze shockcord was out of the way of everything (that's in one of my pictures you uploaded for me).
I never saw one of the spinnaker halyard tangs fail and I've seen some flying kites in very strong wind. Including one on San Francisco Bay in something over 25 knots-the day before racing just sailing the boats from assembly at the Presidio beach to Pier 39. A puff pitchpoled them while both were out on the wire and when the boat was righted the only thing left of the chute was the red, green, and blue tapes around the edge with the rest of the sail draped all over everything-also only about a 1/4 mile in front of an aircraft carrier with the crew lined up on the deck. Others played around in even stronger wind one day at Annapolis with again some pretty spectacular pitchpoles but not a single failed tang.
The "stock" chute was very small compared to what folks ended up using. ProSail had a Minimum required size, so they ended up being HUGE. The tack could easily be pulled all the way to the back of the wing even with the longer poles. I've used the kind of system MBounds is talking about on smaller planing hull monohulls, but I'm not sure I'd feel comfortable with pulling down a chute as big as these with a takedown line. I'd be afraid I'd end up running over it with my wife handling it. Gathering in the foot behind the main and stuffing it goes fairly quickly but of course not like pulling it in while still on the wire.
Try yours in light wind. It's not that hard to deal with and no question adds lots of horsepower.