Fun challenge. Meticulous and systematic approach is advisable.
The only thing that I disliked were the unnecessary distracting 'unused bits'. If they were added to make it harder to solve, I'd have much preferred a tougher consistent 'scheme' instead!
Really stuck in here. Got all the differences, put them into binary but my text is still scrumbled.
And what to do with the extra words? What to do with the _....._ marks.... I know why the differences are there and still can't find a clue.