hydraulic lifters are like little pump up shock absorbers. They rely on being full of oil to pump up and not click.
If they're clicking, they aren't getting enough oil pressure inside. The usual problem is gunk from dirty engine oil blocking up the little holes that let oil into them. Any of the gunk cleaning fluids in Auto stores should fix that. But remember that a strong solvent like that which can eat gunk might also eat other things ( like rubber seals ). Read the label carefully.
Another problem may be that they're worn out beyond repair and have to be replaced. Lifters aren't very expensive. But you have to get the valley cover off to get at them in a V8. Once the push rods are out, you can pull the lifters out by making a hook in the end of a piece of spring steel wire, get the hook into the little oil hole in the dish shaped top of the lifter and pull it out.
Taking apart a fuel injected engine is as easy as a carby engine. Just make sure you take the injection stuff off in as big a sections as you can so that it's easy to reassemble. Make sure all the sensors are properly plugged back in and take a heap of photo's with your digital camera before you strip it.
