You can either import the QT in an SD project and transcode the file once you’ve switched over to the HD projcet, or you can just import it directly into the HD project. Personally, I would just import it directly into the HD project, select “Do no resize smaller image” to maintain the original frame size and use “resize” or “pan & scan” to manipulate the QT from there.
To scale it to 1920×1080, choose the “Image properly sized for current format” option on import. This will alter you aspect ratio and cause some resolution issues, but that’s how it goes unfortunately.
If you have access to a Teranex (or any other uprez hardware) & Beta deck, I would lay the QT to tape and then digitize and uprez via the Teranex. That would be the best way to retain resolution, but most people do not have that equipment laying around.
Hope this helps.