Here is the only company making this kit and I hear that their quality is questionable.
http://www.speedomotive.com/ps-127-1...roker-kit.aspx
After speaking with many Cleveland builders no one recommends going over 4" stroke. Keith Craft only recommends 393's.
Tod Buttermore will also be producing a 9.5" deck block at some point which should get you 460ci, pair that up with some nice CHI heads and you should easily make 700hp. A 408 will get you over 600hp with these heads.