The problem here with acertaining the actual cause. It might be impossible. All that may be visable now is the residual damage.

It may be almost impossible to tell what went out first. I would think without actually knowing that a lifter shattering is not only very unusual but I am trying to remember if I ever even heard of that type of failure before. . Certainly without something else failing first if it were to occur. It takes substantial force.

If the cam is not broken ahead of the number two valve how did the number two valve get bent? So I assume the cam is either broke ahead of the second valve as well or the engine has jumped chain timing during the event.

This event could have occured by the towers that support the cam not being in line accuratly bearing wise. Or more likely there is a specific sequence to removal and installation of the camshaft towers pecular to the 603s that may not have been followed correctly..

After putting the towers back on the engine I would want to hand spin the cam to at least have an indication there was no binding prior to installing the rockers. It also may have been damaged at the time the towers were taken off the head.. I doubt if anyone checked the camshaft at any time for any runout. I guess what I am trying to state that if you do not have the service information or knowledge on working on the 603s you could damage the camshaft.

I would not discuss this with the mechanic or the head rebuilder. Your lawyer could prevail in discovery by asking the mechanic or machine shop the sequence of or methology used in removal of the cam and towers.

If whoever removed the cam etc does not know the required sequences you have them.They are probably very confused themselves about what transpired. Not an act of god without following the correct methology. Best of luck.