Could Harn work in the Hyborian Age, dropped of the west coast of the Pictish Wilderness? Both are fantasy worlds that incorporate anachronistic Earth cultures. Can the gritty realism of Harn be successfully mixed with the gritty pulp of the Hyborian Age?

This would be the Hyborian Age of Howard's novels and select pastiche, not the Hyborian Age of the fur loincloth Conan of movies and comics.

I don't see why you couldn't if you wanted. The problem I would have using it for S&S would be the adventurers being there for ten minutes before they take ship to continue the pursuit of the Zingaran kidnappers to recover one of the heirs to the crown of Kaldor. I'd have to try really hard to keep the PCs there in a "serious" genre simulation campaign.

You might want to poke around here for the Cthulhu Harn fanon some feller wrote up... it would be a good addition to the sort of pHarn you are proposing.

I have that Cthulhul Harn fanon filed in my hard drive - thanks. I do liberally mix Howard and Lovecraft, both in the Hyborian Age and in CoC.

Really, I think the problem is that I'm trying to find a replacement for Kethira because it isn't very well developed and I don't think that's going to change in the near future, if ever. That would be great if I wanted a more or less blank canvas that I could develop myself, but because of time constraints I'd like a more developed setting.

The Hyborian Age comes to mind because as I look at developing Kethira myself I start plugging in stereotypical earth cultures (Shorkyne = France, Trierzon = Spain, Dalkesh = Egypt, etc), which is what Howard did. The flavor is definitely different though.

I've also considered using Harn as a mythic Earth's Hy Brazil, say somewhere between 900 - 1200 AD. The problem with running it as a "lost island" is it then becomes very cut off from the rest of the world.

The Harnthulhu thing is what came to mind first. I don't know that the world outside the Misty Isle is all that under-developed, but I suppose in comparison with Hyboria's recent ConanD20 treatment it is just that.

For my part I was considering going more the direction of Soloman Kane than Conan, but I have to find some players and the time.