How many miles is on this 94 4.3L?
It's probably not worth dumping the money into. You can start with the simple things. Pulleys, wires, plugs, ignition system, air filter and exhaust. Run 2" exhaust (duals) cuz you don't want to lose any torque by going to big.
If you want to dump the money into the thing, go for shaving the heads, replacing the cams and look into a supercharger (I like these since you get power from the get-go).