Seems likely that people are bringing different expectations to this idea. For any even remotely modern tether car, you probably have to have a serious track. But that is not where the conversation started--with the wooden car powered(?) by a GHQ. For example, a couple of years ago during one of our control line airplane races, we had some of the tether car guys (there is an active and excellent track at Whittier Narrows park here in LA) ask to use our paved flying circle during our lunch break for a vintage car demo. There was no conflict, and besides, we wanted to see what a vintage car could do. As I recall, they brought out a weighted pylon and gave it a go. Seemed to work fine--but it was going at a speed that you could watch it go around, as opposed to the modern cars that are just a blur. It was fun....
I do not recall how long the line was, but again if I recall correctly, it was attached to the pylon a few feet off the ground.
You could probably get any and all advice you need from the tether guys. I suppose they have a forum? They love vintage stuff. I went to their NATS a few years back, and they had lots of cars on display. Not a wooden one among 'em though. But they sure had lot of rough aluminum castings for car bodies.