I am interested in the same 400 RWHP. I am currently at 372 with Headers, Honker, and a Tune. The tuner I have been using, Sean at OCC, recommends the FAST, and 1.85 Roller Rockers and he said I should be at 400 RWHP or slightly above. I am pretty sure the rockers will void my warranty on the engine, and I have read many post with widely varing opinions on doing the rockers. So I am still in the research stage and am planning another trip to go talk to Sean about the rockers and other options. I will be interested in the opinions you get here.
Good Luck
Good Luck