You bet I am.
I'm running more or less published Cthulhu adventures (from the Gaslight stuff) and then modifying them a heck of a lot. I see opportunities to throw in bits of my own storyline, and do so whenever I can. Sometimes this leads to tangents (like where we are currently; the actual published adventure wouldn't pick up until you're at Avebury, so this is all free-form), but that's ok.
The whole thing in the last chapter about Mary Kelly and brain surgery came from Arthur Machen's "The Great God Pan". In the first chapter of that story it had about a doctor who did some sort of brain operation on a servant, said servant becoming pregnant shortly thereafter. I figured since (at least to me) the story's events seem to be a thinly-disguised version of the Ripper anyway, I may as well finish the job.
Langan's stone with the Latin inscription also came from the same story word-for-word: in the story, it's a stone pillar at Lydney.
The last chapter was based on a Chaosium adventure, and the woman at the end was originally one of the serpent people. Initially, I was going to have Queen Tera appear as Mary Kelly (in fact, at one time I was thinking of playing off of the theory that Mary Kelly was not, in fact, murdered and making her a part of EIECET's group), but later I decided on Madame Sosostris. As far as I know, Sosostris was not real, although she does appear in "The Waste Land" by T.S. Eliot and later in several Cthulhu stories.
Dr. Bond's suicide did happen, though I played with the timeline a little bit. The real one happened in 1903, I think.
BTW, I'm going to run another Victorian-era game on another forum, and although I can't exactly follow the plot since one of the players knows
things about this game through conversations with me, I think I'll at the very least have EIECET, Langan, Harrington, and your characters pop up.
Hawksmoor is very weird - I intially heard of him during Jack's "tour" chapter in Alan Moore's
From Hell (my favorite section, surprisingly for me) and later picked up some Iain Sinclair stuff in which he alludes to the possibility that maybe the churches had something to do with the fact that these murders happened where they did.