I have a 79 12A :

when I put in a header do I need to take off the heat exchanger? or I can leave it there? because I know it takes some HP but not much so if I can leave it there I would.. if I would put a RB Header, keep the heat exchanger(cuz I don't wanna feel dizzy after a while) and get my self a custom exhaust do you guys think my exhaust will be too loud? and people are talking about a ACV and air pump can I leave those on too? should I?

With the header/collector and full stainless muffler I should be set for a good 20HP?

 

You don't need to take the heat exchanger off, the header bolts to it...The general opinion here, though, is to replace it w/ a presilencer. I don't think it'll be too loud. Remove the air pump and bracket...you'll need to take it off to make room anyway...