You can use a number of turbos that will make over 400ho on the stock manifolds e.g. Gt3076.
However I would be looking at something from Hypergear - have a look at his thread. What he does like to do sometimes is weld a mount for a wastegate on to the stock exhaust manifold. Just get your tuner to have a look at some of Hypergears latest products which are often used with stock inlet and exhaust manifolds to make way in excess of 400 hp. Mind you he uses a very good tuner...
e.g. 560 hp on stock manifold (mind you that's on e85, a little less on your pump gas).