Our wing supports stuck a little forward of the mast stump, so the obvious place to put the track was above that. You don't have that barrier, so the track can go lower, which means an easier time attaching the ends of the track. The Atum method was a 30mm length of carbon tube on each gunwhale, carboned down. The track was threaded through the little tubes, attached in the middle, the tubes were bogged down and later carboned.
On Antidote, because the gunwales are lower and the centre of the track is higher, there are prominent ears to support the end of the track. This was tricky to get right.
If you try the Atum method, the good bits are no ears, and an easier time fitting the track because it can be fitted without cutting it. The risks are a lower jib may have trouble getting over the kite hoop if yours is prominent (though a lower jib is good for other reasons), and a lower jib track may obstruct the spinnaker a bit in the sock as it dropped.
As far as angle goes, ours is probably about 60 degs to horizontal, and I am reasonably sure that a straight up one would work.
Theory is as follows:
1) A jib clew has two edges coming into it: Leech and Foot. Topologically these are the same (that is you could have a jib where the foot and the leech are the same length)
2) This means that the fundamental angle of a track is 'relative to the bisection of the angle of the foot and leech' rather than up or down.
3) The major issue with jib tracks is whether the car goes right to the end or not. If not, then you have a problem like rope self tackers.
4) If jib tracks flat on the deck work, it follows vertical ones will work too, especially as leech tension is at least as much as foot tension in a jib.
