Basically I did what the tutorial elsewhere on this forum suggested. I recently downloaded a newer version, and plan to try undoing my in-TV tweaks and see if SwitchResX alone can do it. (The tweaks are pretty minor, just a few pixels up/down and left/right, but maybe SwitchResX can do 100% if I try.)
In my case, I set it for 1366x768. My TV is officially 1024x768, but since the pixels aren't square 1366x768 is the logical square-pixel equivalent. Made a world of difference.