I've read a fair amount of digitized published 18th century texts, which were presumably edited by the 18th c publisher. And yeah, of course those are different from modern texts in capitalization, abbreviations, contractions, some spelling, long s, etc. But O'Sullivan's text is different in that presumably no 18th c publisher has been at it. It was in the Stuart Papers, so I assume it was hand-written, and the 20th c editors seem to have done a great job in preserving the way he wrote.