That's super helpful! Thanks! Weirdly now if I set the project to 640x480, the "analog damage" filter greatly distorts all the white on black captions so I'm trying to hunt that down! If I delete and replace the text it's fine but I'm trying to avoid having to manually do that for every caption!
EDIT:
I just went ahead and manually fixed them all as troubleshooting was taking longer than just replacing them.
Howard Roll wrote:NTSC pixels aren't square they're rectangular. Going to an NTSC aspect ratio from a square AR requires a correction to be made. Exporting 720X486 is only 4:3 (40:29) when exporting with an NTSC aspect ratio (rectangular) pixel. What you're exporting is 3:2 not 4:3. For a square pixel 4:3 image you'd need to export 640X480, 800X600, etc.,
Good Luck