Thanks George and Larry. I think you both identified the part. However, it is not the root cause of my lifter damage because the flange on my distributor is in place and intact (photo is below). It looks like that cracked flange has been laying there for more than two decades.
My next step is to pull the cam and asses the damage to the lobes for cylinder #4 along with any collateral damage. And the precipitator of the problem has yet to be found.
