Thanx for leads, but I don't have the DynamicTwinView option in xorg.conf.to comment out. The nvidia forum suggests problem with driver and kde's(?) xrandr version. So I can ignore the kde control center 50-54hz persistent figure.
Clicking through the nvidia-setting applet revealed an "advanced" button giving a 75hz option to set with the detected AL1714 monitor at 1280x1024. It also appears that saving this setting caused the VideoRam number to be commented out in monitor section of xorg file. The desktop otherwise looks fine and after rebooting I don't need to hit the auto set button on the tft monitor to center the image.
Thanx again all