JAC Jerry with an FE motor a back off the rocker shafts every year at the end of the season. I don't have the comp cam spec sheet on all the valve springs but only a few are good for cam shafts over .600" lift. If you have time and can run the motor until fully warm, pull a valve cover and get a feeler gauge and check for coil bind. Comp said that .100" is min. I know guys running 1/4 mile with .060" clearance. Have not seen them break them but after the season, new springs are installed. It is possible that you do have a bad valve spring and nothing more. Have you called Ford racing and ask about this issue. This would be a good place to start. Call them and say you where breaking in the motor on a engine stand (NO DYNO CELL) and tell them what happened. If nothing else try and get the part# of there valve springs. I have a funny feeling they are cheating with a spring and a .580" max lift spec and going to over .600" and hoping the .020" is not going to cause a problem. Also was your motor a new block or recycled one? In hind sight maybe this just saved you another $7,000 + motor replacement.
Rick L.