Just tasted Old Viscosity for the first time tonight at Lost Abbey. Have had the opportunity at port brewing a bunch of times but never did partake of it. Well, that was a mistake. Phenomenal brew. Not quite sure what to make of it in terms of style. I would put it somewhere in the area of a Russian Imperial Stout and a Barleywine. Definitely not belgian yeast. I would suggest some crystal 120, chocolate malt and carafa III and maybe a mix of notty and WLP001. They use magnum, a clean bittering hop. I would guess not more than 40 IBU. Not sure how you get the viscosity, which, of course, is what makes it old viscosity. Maybe a bunch of Carapilis. They say shoot for somewhere around 1.09 OG. A reasonably large dose of dark malts and crystal. The recipe might be a lot like Old Rasputin with less hops but I certainly don't get the mouthfeel of that from my recipe.
If anyone figures it out, I'd love to know.