272-276 lines (pixels) seems to be a common size for a letterboxed NTSC source and would be defined in the telecine process. And for a LB PAL source it would be 326 lines (pixels). And these numbers should remain the same even if the source was transfered to another format, without any vertical resizing of course.

Comparing with the ROTJ Faces LD it seems both the PAL and NTSC GOUT have been vertically resized and cropped. The LD is 276 lines high, the NTSC GOUT is 274 and shows less information both top and bottom more less than the 2 lines difference. The PAL GOUT is 326 lines high and shows the same amount of info at the top as the LD but is cropped 7-8 lines more at the bottom.

Only LFL knows why it was done this way, there's really no technical reason for it. Making the PAL GOUT from the NTSC source only require a simple vertical resize from 276 to 326 lines and adjusting the black bars to fill up the 576 lines of a PAL DVD picture.