Yeah, if you don't have to pass emissions, take it to an exhaust shop and have them put you in a 2.25 or 2.5" dual exhaust without cats. That will really help to open the engine up. I'm sure the carb could use a rebuild. How does the distributer cap and rotor look?
After the dual exhaust and carb, the next step to take would be the cam. These three items will really wake that thing up.
well, the first, and obvious thing, is a full tune up, plugs, wires, cap&rotor, fluides changed, PCV valve, filters etc...
then, throw on a 14" open element air filter. Atleast drain the beats fromt he cat. or spend the money and have a nice exhaust put on.
rebuild the carb, unless you are going crazy with a mega power 500, the stock Qudrajet is perhaps the best carb to slap on the 500, don't let anyone tell you otherwise.
Do a search for "472 intake modification" and you can remove your intake manifold, bring it to a machine shop, and they should be able to remove the center section, that'll be good for a small chunk of power.
Of course a cam would help, that that will move the power band up, not what you want if you want more low end torque... plus, you may be getting more involved changing the cam then you think.