Headers

I think I already now the answer to this question but I'm going to ask anyway.
I'm looking into building a 470 . I'm wanting about 500 HP ,NOW how much would the stock exhaust manifolds restrict the engine. I don't plan on racing . I'm asking because I've done a lot of reading and research on headers (Shumacher and TTI ) and fitment . Both sets are expensive and Shumacher being the better as far as instillation . Like most of us
I'm building on a budget and if the stock manifolds will work with out a sharp decrease in HP why not use them. Also looking for any other practical application that will work.

Zigs