I'd start with a cap kit, but that is some pretty severe positioning problems. Also try playing with the horizontal width coil to see if that does anything useful. I don't know anything about a Sampo monitor, so can't help you with exact specifics.
The OTHER thing you could do is to flip the yoke wires to rotate the image 180 degrees, and see if that helps centering, but then you'd have to rotate the monitor in the cabinet.
I know I've done this on a Wells Gardner K4600 monitor that would not display Arkanoid II jamma board correctly on one orientation, but flipped the yoke signals and rotated it and it fit the screen much better.
Post if you need assistance in flipping the yoke correctly.