Welcome to CHR! Nice Chevelle! Like techinspector1 says it's not a lightweight, so it really depends on how much you want to spend, and how much fun you're talking about. You'll probably get a bit of noticeable performance increase from a set of good headers made specifically for your setup, one of the old line main brands, but before I put very much money into the 327 I'd look at boosting the engine size, or even going to a later model takeout engine, tranny and electronics from a newer Camaro or ??? The old adage is even more true today...
Speed Is Money, How Fast Do You Want To Go?