The 5.4 doesn't have pushrods or lifters. It has overhead camshafts with cam followers and lash adjusters.
It is weird that it only does it when decelerating. I wonder if there is a small exhaust leak somewhere causing the noise.
They are not adjustable. They are hydralic like a lifter. They take up the lash between the cam follower (like a rocker arm) and the valve.
I have never had one of these engines apart yet, but I am sure that they are similiar to the TurboCoupe T-Bird that I did.