It is the new Boss block that came out a couple of years ago (I think). I've been told it is rated at 1200 hp but have also heard 1500hp. I'm also told that required different head and timming chain cover bolts. This block compares to the dart sportmans.
http://www.svtperformance.com/forums/road-side-pub-17/592919-better-boss-block-dart.html
gotcha. :beer: