Cheap Torque from 5.7L

Just bought a 1992 Chevy K2500 with 160K on the original stock motor. Runs fine but seems flat. Meaning it will go when you really stomp it but it is not very responsive - feels like it can't breath very well.

I don't want to put too much into the motor, but would like to know what $500 would get me. I am most interested in low and mid range torgue.

I was thinking about a K&N intake, Flow Master cat back system and a performance chip.

Questions:
Will this *brighten* the performance and give a more responsive feel?
What kind of increases in HP and Torque can I expect?
Will headers add much more?
Is there a better way to spend the money?

Links and specific answers would be greatly appreciated.

Thanks,
Doug