how much hp would i gain from port,polish,and shaving my header?

 

Do you mean your stock header and exhaust ports?

 

yes i do

 

I can't be specific but modifying your stock exhaust manifold would probably not be worth the effort.
If you were going to enlarge the exhaust ports it would be worth your time to remove the head, have a real port and polish done, and install the GT cam this would be worth the time and effort.
Do not whip out your dremmel and try to enlarge your exhaust ports. You would run the risk of really screwing things up. Also that would be a PIA to accomplish. You would most likely have to remove the head anyway so why not do it right.
Then after that get the header of your choice and follow that with a good exhaust set-up.

 

thanks for the advice design