There have been some original paint motors 1969 340's that have popped up different colors. With strong documentation to back it up. Very few though.
But they are oddballs. You can't say all 4-speeds were hemi orange. That's way over-reaching. Many people in this thread have 1969 340 4-speed that were not Hemi Orange.
If you don't have solid proof you motor was not turquoise, then keep it turquoise.