I ran something similiar (in that it was an alternate SR timeline, not that it was
Shadowrun by Gaslight or anything) a year or two ago, which I called WW2SR. The idea being that the Awakening had come in the year 1911, rather than 2011, and by the outbreak of the Second World War, metahumans and magic had become if not commonplace, then accepted and exploited.
Mechanically, there was no Cyber or Bioware to start, and the cost of Magic Powers for Phys Ads were doubled. Drain was calculated at full for Mages, instead of F/2. Metahumans were Priority A, as were Full Magicians, just like the old days. Cyberware, had I run the game long enough to introduce it, would have been at x2 Essence, and would have looked a heck of a lot like the stuff in Return to Castle Wolfenstein for the PS2. Which is not that far a cry from Steampunk.
I have thought from time to time of running other games, each time running the calendar back 100 years, having the world Awaken in 1811, 1711, or just whenever I felt like it. I like keeping it in the something_11, because its easier to update the timeline, and it gives the players something familiar to latch onto.
Some of my players grokked the idea, others it just made want to play normal SR since we had been on a break from it for awhile. So I only ran four or five sessions, starting out with the raid on Dieppe in 1942, the capture and escape(?) of Hess, and then to the Pacific. Other things I had wanted to run were Stalingrad, the Normandy Invasion, the Siege of Malta, and the Fall of Eagle's Nest. (At least, I think thats what they were called, its been a few years and I don't have my notes in front of me.)
Sometimes when we're making adventures, these leaps in logic or creativity seem natural to us. Combine playing RtCW on the PS2 with renting Band of Brothers and Enemy at the Gates and the idea of mages landing in Normandy seems fairly natural. It is sometimes a harder leap for the players to make, especially if they are more familiar with one part than the other. I don't want to be a naysayer, but its a hurdle I ran into, so I thought I'd mention it.
As for inspiration, I get a lot of inspiration from the movies.
Wild Wild West and
Van Helsing were both horrible, but Steampunk and Gothic Horror are the new Fantasy Movies, meaning that they all suck but what choice do we have? I'd also include
From Hell and
LXG, even though you'd probably do better and go read the originals. (I considered LXG to be the most disappointing movie of that year for me, not that it was horrible, just that I had expected so much more, which is my own damn fault. From Hell I liked, all except for Heather Graham, who was about as convincing as a turn of the century prostitute as my dog would be, albeit for different reasons.)
There was a Batman Graphic Novel called Gotham by Gaslight, I only read that one and I don't know if there were any others, and it was just okay.
One suggestion, borrowing from the LXG graphic novels, is it would be neat to see various literary and historical figures done up in SR style. I'd be tempted to make Sherlock Holmes as an immortal elf, myself. Perhaps Dr. Jekyll invented a serum that would turn him into a troll for a short period of time. Dracula and the wolfman already have stats (vampire and loup-garous), the Frankenstein monster is a cyberzombie... as a side note, in my WW2SR game Max Shrek was a real nosferatu and the head of some Nazi Special Weapons Bureau, making vampiric pawns to compete with the SuperSoldat cyberzombie program. Continuing on, I could see making Tarzan a phys ad. Its tricky to fit the metahumans in, but I guess all it requires is making a leap of faith. I could see making Van Helsing a dwarf or an ork, likewise I could see Frankenstein's monster starting off as a troll (it would satisfy the doctor's requirement of needing a big body to work with, and it wouldn't do to have pc's bigger than the monster.)
Anyhoo, I'm rambling. Sort of brainstorming by scattergun effect, firing wildly and hoping something hits.