Sorry I went silent. I've been too busy to even check Mastodon, let alone post on it.
Today, however, I self-nerd-sniped and implemented a one-click aspect ratio correction userscript for 320x200 screenshots of DOS games on MobyGames:
https://greasyfork.org/en/scripts/400983-mobygames-click-to-aspect-correct-screenshots
(See https://www.gamasutra.com/blogs/FelipePepe/20150423/241730/No_MSDOS_games_werent_widescreen_Tips_on_correcting_aspect_ratio.php for an explanation of why it's necessary.)