Yes, I'm aware of the issue with the rocker shafts, in fact, until I got into trying to get things repaired after the tow, that's what I thought was the problem.
I'm pretty sure the sequence of events went valve head separated from the valve stem first, it's hard to tell from the angle of the picture but the head looks like it just broke off at the base of the stem (where the 2 are bonded). this let the stem go back up the guide but due to build-up and taper at the end of the stem where it broke, the stem stuck in the guide, on the next revolutions the rocker could not depress the stem and this caused the rocker shaft to break at the known weak point. With the head of the valve now loose in the cylinder when the piston came back up it jamed and caused the piston to deflect to the side which broke out the side wall of the cylinder.
When I put the 2 pieces together they line up perfectly straight with no deflection in the valve stem , which would not be the case if the head had contacted the piston plus when I look at the piston the only marks on top are where the valve head was stem down on the piston when it came up.
So lessons learned so far
:
If you have an FE replace (at minimum) the rocker pillars with upgrade pillars that provide end support (best to replace the entire rocker assembly).
If you are having an engine built, or purchase a "rebuilt" engine using iron FE heads make sure the valves are/were replaced with stainless steel (min.)
406 FE is a very rare engine with lowest production numbers of all FE's, as the result it's $$$ to repair if you need new pistons
later,
mike