When you capture lossless AVI, everything is displayed in Square Pixels (1:1). So the reason NTSC looks "stretched", this is the cause, as literal 720 pixels wide and 480 pixels high.
Now when you pop in an NTSC DVD file, do you notice that the resolution is 720x480, but it's being displayed as 640x480? This is because the pixels are being assigned a flag to display in 4:3, adhering to the laws of NTSC video standard without resizing.
To do this in Hybrid, go to Cropping and tick both boxes "Force Input PAR" and "Force Output PAR"- type in 8x9, this is MPEG-2 NTSC DVD ratio, but it's also appropriate for SD AVC files. When you do this, you retain the resolution but you change the "shape" of the pixels- so they're no longer square, but a ratio that matches with what we see as 4:3. Make sure your resolution is 720x480 all the way through.
In terms of YouTube, you want to have the size as 1440x1080, 1:1. The reason for this being is that if you have it any lower, your video quality will suffer worse from the compression compared to how it was. Make sure you deinterlace properly as well.
Important; for YouTube, follow this encoding specs guide provided by the site- all settings configurable in Hybrid. Hope this helps!
https://support.google.com/youtube/answer/1722171?hl=en