Dyno Results Question??

Hey guys I have finally begun my performance work on my 351 Windsor this summer. I am just waiting for my headers to get here so I can set up my Dr. Gas 2.5" X-pipe system and spintech mufflers. Currently I have dynoed at 155 rwhp I am at 5000 ft elevation in Utah though. What kind of gains can I expect from bolting on that exhaust system. I wanna dyno again afterwards, but just can't afford it because I am saving up for performer RPM, new cam, afr 185's, and gas prices. I will dyno again after all of this has been done. I was hoping the exhaust system will shoot me up to around 180 rwhp. What can I expect guys?? I will keep you guys posted as I continue to build my engine.

Crap I don't know all of that. I will figure it out in a couple of days though. Give me the exact specifics that I will need to get.

For starters, I have a holley 4010 600cfm carb, with bone stock engine except the manifold which is a performer 351.