FOUND! ARVIN 9219-cm-uhf television.

[old_tv_nut]

Linearity usually affects left side vs. right side. If both edges are too narrow or too wide compared with the middle, this is usually due to the size of "S correction" capacitor in series with the yoke. I can't recall off the top of my head which makes the sides narrower, smaller S cap or bigger, but I think it's smaller for narrower sides.

You could try jumpering a small cap (10% of existing one) across the existing one to see how things change.