Since there has been some discussion on cage height, design, etc. Thought this image of Sheldon Kinser's Grant King car from 1974 was interesting. Notice the heigth of the cage. Sheldon was a tall guy too.

Sheldon's head stuck three inches above most cages in the cars I seen him in.

After a series of flips/barrel rolls how much will a set of belts typically stretch??

Something else to keep in mind is that the spine and neck also stretch during a flip or roll due to centrifucal force generated by the mass of the head and helmet.

Belts can stretch 20% in a hard wreck. They move some when you are racing. That's why I pull my shoulder belts down at every yellow.

One of the Heartland Racing Association nw cars has an extra bar welded to the the sides and back of the halo. Looked like it added 4-5 inches of additional clearance across the back. May have been the Ned Powers car, not sure. They were supporting series at Jackson, running with NSL Wings.