The VT320 terminal has a “width” adjustment coil – but on one of my terminals at least it coil does not offer a very good range.
Something degraded (or de-magnetized) over the years and made the display much narrower than it should (has been).
L201 is an adjustable coil marked “WIDTH”. It is placed in the circuit in series with L202 (“H-LIN”). To extend the horizontal range, a magnet can be placed on top of coil L202. This offers a constant width offset in a range not achievable by trimming using just L201.
I used a 1/8″ rare earth magnet (Radio Shack 641895), but any similar strength and size magnet can be used.
Here is a screen shot showing the best achieveable width using just L201:
L202 can be seen at the center of the photo:
Here is L202 with a magnet stuck on top, and the resulting image:
The resulting image is actually shrunk narrower. So flipping the magnet caused it to expand: