The primary source of the ‘despecialized’ versions are from the Blu Ray videos. If you are looking for versions of any of the Star Wars Theatrical cuts that have more picture information, you’re best bet is to look for the fan-made 4K versions–‘4K77’, ‘4K83’, and ‘Renegade Grindhouse’ of ‘The Empire Strikes Back’ as ‘4K80’ is in production. These 4K versions are available in UHD and 1080p. The sole source of these versions are made up of scans from multiple 35mm theatrical prints. Although there is cropping in these versions, too, the final releases do have more picture information than the current Blu Ray versions.
Then, should I just upscale the version from the 2006 DVD print?