I honestly don't think Black Dahlia is on this again, I really think they are on Mayhem Fest. Bodom is definitely a contender to headline and I can totally see Gojira doing this as well. As for Oceano, Just no. I can't speak for the rest of the country, but Oceano got a tepid crowd response at Summer Slaughter 2011 here (Only them and Six Feet Under got a lukewarm crowd responses). Personally, I really hope they're are not on there. Their live show has gotten remarkably worse and their set at NEMHF last year was absolute torture (Worst sound mix I've ever heard, It sounded like a fucking disturbed beehive.) I fully trust Ash to put together another great lineup for 2013, Summer Slaughter hasn't had a single bad lineup to date imo.
3/14 Dropkick Murphys
4/10 At the Gates/Converge