keep the open element air cleaner for a start. second as a set of crinkle black valve covers. check the current ford motorsport catalog as they have a number of nice sets. i suggest the ones that say mustang powered by ford.
next clean up the engine bay by hiding the wiring as much as possible. some guys use conduit that runs behind the inner fender panel to run the wires in to protect them. you can also add a set of colored spark plug wires, anything other then black. accel makes a nice yellow set, and msd has a nice red set. there are other colors available as well just check with summit racing for different ones.
you can step up to a set of chrome pulleys as well, or go with billet aluminum ones. again check the ford motorsport catalog.
an aluminum radiator will also dress up the engine compartment by adding some flash. add to that a flex fan, or better an electric fan for a high tech look.
then you can move the battery out of the engine compartment into the truck, that not only cleans up the engine compartment, but changes the weight distribution for the better as well.
you can also repaint the engine compartment body color, or even carry your exterior paint scheme into the engine compartment.
my mind is aglow with whirling transient nodes of thought careening through a cosmic vapor of invention.