I have an 86 z-28 w/305 stock. I believe it's a push rod hitting, because it can be heard when I start the car and also as I increase power the tapping/knocking goes faster. My question is how do you change one? Thanks for any help provided.

Take a piece of garden hose and put it to the valve cover and listen for the tapping sound. If it's a lifter, you would be able to here it throught he hose. How does the engine idle? Is it rough? Another possibility is an exhaust leak on the driver's side.