If I put a custom dual exhaust on my '84 caprice 5.0 305 will there be a noticable difference in power? I have the resouces to make my own custom stainless steel exhaust system. Thanks!

No.

What if I were to include headers? I have a set thats been sitting in my garage for the longest time.

I would just do it for looks and sound of badass'ness.

Just do it.

The power increase would be negligible, but it would sound bad-ass. Are you absolutely sure your headers will fit your application?

yup

Cool !

What kind are they?

I'm not sure what brand they are, all I know is that they're stainless steel, and were custom made for some guy at this muffler shop down the road from me, and he never paid for em, so the manager there sold em to me for $50 (after I made sure they'd fit my car).

I did it on my 84 Monte SS and it did make a difference however slight.
I started getting better power numbers when i did the intake and carb.
then i built a 350 with about 325HP so the exhaust paid off in the long run...

Awsome