I don't really know what I'm talking about, but would it be possible to replace whatever part of the analog circuitry is responsible for the horizontal scan rate?
Also, just because the vertical resolution is different doesn't 100% mean that the horizontal scan rate is different. You also need to consider the number of invisible lines in the vblank region. For instance with VGA at 640 x 480, there are actually 525 lines, but 45 of them are invisible. So if the total number of visible + invisible lines is similar for 9" B&W and 12" RGB, it might still be OK.
I just looked it up, and the 9" CRT has a horizontal scan rate of 22.25 kHz, while the 12" RGB has a horizontal scan rate of 24.48 kHz. That's a difference of about 10%, which is a little better than the difference in the vertical resolution, but not by much. Hmmm.
Also, just because the vertical resolution is different doesn't 100% mean that the horizontal scan rate is different. You also need to consider the number of invisible lines in the vblank region. For instance with VGA at 640 x 480, there are actually 525 lines, but 45 of them are invisible. So if the total number of visible + invisible lines is similar for 9" B&W and 12" RGB, it might still be OK.
I just looked it up, and the 9" CRT has a horizontal scan rate of 22.25 kHz, while the 12" RGB has a horizontal scan rate of 24.48 kHz. That's a difference of about 10%, which is a little better than the difference in the vertical resolution, but not by much. Hmmm.