What nkowi said. Drive it till it pukes. I doubt it will, because I doubt their diagnosis.
My 4.7 has over 230k miles. The valve train sounds like a bunch of marbles in a coffee can and it keeps right on running, day after day. For what it's worth, the 4.7 uses chain driven overhead cams. Instead of the cam acting directly on the valve, they have it acting on a rocker arm.
