Instead og the adjustable trap height systems out there, (and there are some good ones), I like the dogbone rings, or the keyhole looking rings.
This gives two distinct places to hook in, which ever id chosen just befroe trapping out. they are usually 4-6 inches apart, allowing for two distinct heights.
True. In fact that's the system I have. I didn't think about it when asked about an "adjustable system"

I have dogbones with two distinct holes. I don't even have a pulley, the line just slides in the eye of the trap line, I don't think you can do a trapeze line with less hardware.
Talking about trapeze, what trick do you use to connect the tensionning shock cord to the trapeze line? I use a knot, but knots on shock cord have an annoying tendency to invert and slip, even when taped...