How can you get more HP and Torque out of your 1990 460?

For starters make sure the engine is running at peak performance, meaning it has good compression, no vacuum leaks, and the entire ignition system is in good order.

After that, depending on what you want to get out of the motor, you can start with a K&N air filter and some dual exhaust. This will let the engine breathe easier.

Then after that you can go with a camshaft, new heads, headers, etc. If it's computer controlled you might be able to get a chip or programmer for it.

Need more info though. What is the engine going to be used for? Pulling a boat or camper? Drag racing? Is it in a car or truck?