I found a manual for this monitor. It is a 3 position jumper

. That's some sweet fine-tuning control right there. Thanks Wells-Gardner.
So it is about an 1/8" off center now, and I guess that is as close as it is going to get because WG didn't want to "splurge" for a pot.
I have another question though regarding the horizontal width coil. Which direction (CW or CCW) do you turn the allen-head screw inside to make the picture wider? I have it all the way CC right now, and earlier I turned it maybe 6 or 7 complete turns CCW and it didn't seem to make a noticeable difference in the horizontal width. I didn't want to keep going because I don't know if that allen head screw will turn indefinitely or simply unscrew and fall out, so I turned it all the way back CC and left it. If I could make the horizontal width about a half inch wider, the picture would be close to perfect aside from being vertically off-center by about an eighth of an inch due to that crude 3 position vertical shift jumper adjustment.