Okay, so I've completed the subtitle removal today. There are 28 subtitles in the film, and removing them was time consuming. I used individual masks for each subtitle rather than creating one big mask that would work for all 28. Now I'm just double-checking I haven't made any errors in the frame codes. You can see the sample image I posted back here. Here's the code for it, as you can see it's one big sequential manual-labour effort.
To remove the subtitles I had to de-grain those frames. So, once I've finished checking them I'll use grainfactory to restore the correct grain level for the frames where subtitles were removed. Then all that's left to do is to put in the theatrically-correct subtitles using the Z-VCD theatrical bootleg as a guide for the timing and placement. They'll be burned-in as requested.