On my 360: I installed headers (first thing you should do), along with a new exhaust system with larger pipes and a crossover.
Added a 6-pak manifold (partly for performance and admittedly partly for the visual when you open the hood)
These two Mods really made my small block come alive. (You can use an after market 4 bbl manifold and Carb, if you don't want to go with multi-carbs, and you will not be disappointed)
Also, have a bit hotter cam installed as well. And, a little head work as well.
Just remember that your engine is nothing more than an "air pump" that takes air and gas, mixes them together and produces power. So working on the intake and exhaust will give you the largest return for the money.
It really all comes down to how fast you want to go, and how much money you are willing to spend to get that fast.