A 2 bolt big block or small block will take 500hp.
Do you have a big block? If not, added expense.
New headers, pulleys, brackets, plug wires etc. Possible new exhaust depending on what you have now.
Trans? 350? 400? Big block- highly recommend th400.
383 is a very nice engine.can make great power and depending on the other things, can be cheaper.
496- stroked big block= torque monster!
All depends on your budget and your plan for the car. Cruiser, street/strip, etc.