Lets see here now. You have a lot of places you could go from here. Obviously putting a new motor in would get you a lot! But that is an undertaking that I don't know if you are into. Think about some of these things:
High flow airfilter setup
upgraded clutch (10.5 inch performance setup)
traction bars/under ride bars
export brace, monte carlo bar
shift kit and etc(I don't know much about autos on these)
driveshaft loop (not good for performance, but good to keep you safe)
upgraded ignition, coil, plug wires( pertronix,msd drop in probillit, etc)
IGNORE THE SPLITFIRE AND QUAD POINT PLUGS they are a scam.
If you are really looking for performance you may wish to replace that 600 vac sec holley with a double pump. (my car is now chirping 3rd without clutching it, something that would not be possible with the vac secondaries.)
If you want to go into the engine I don't know where to tell you to start. It is going to make a big difference on what direction to head depending on what you want to do with the car, how much you want to spend, and what kind of time/skill constraints you have. I will try to think of some more.