Thank you, Dez and Jetusenet.
I have adjusted the tab around the yoke magnet and it makes only a minor difference, mainly in the straightness of the image.
I did have the chassis capped by Chad at Arcade CRT...he did an awesome job of bringing a dead monitor back to life. I've only just completed fixing several other issues with the game boards so now I just have to get things adjusted properly.
Thanks for the suggestion about the vertical linearity adjustments. I'll see if adjusting R263 and/or R257 does the trick and I'll report back. Thanks again for the quick suggestions.