Problem solved! Pulled the engine today (really just removed the rad and pulled the engine ahead about 6 inches) and out came the old flexplate. It was original to the car (car has only 20600 miles on it, yes that's correct, 20600 miles), was about a quarter of an inch thick with two spring steel fingers about 180 degrees apart on its outer edge. One of the fingers (held on with 3 large rivets) was somewhat loose. Yes, that's all that was making the noise that sounded like the engine had thrown a rod. The new flexplate is only a 16th inch thick and without the spring steel fingers. Its larger in diameter to make up for the missing fingers. The only puzzle was that the six bolt holes in the flexplate that mount it to the end of the crank ARE NOT EVENLY SPACED. Mark the spacers and their correct side facing the flexplate, the flexplate, and the crank before you remove the pieces or it will drive you to drink trying to put the pieces back in. (Anyone who has put in a new fuel sending unit into their gas tank will know of what I am referrring. The bolt spacings are not evenly spaced there either, to ensure that the float assembly can only go back into the tank one way.) Pulling the engine, replacing the flexplate, and getting the car back together took a full day....but what a change. No more clanging and banging! And I think I can salvage the old flexplate by heating the rivets up and driving them home. Hopefully it will be a long time before I need to do this ever again. Hope this helps someone else out. Remember that that banging engine sound may just be a cracked or broken flexplate. The old timer (72) who helped me break the engine apart knew the sound and its cause as soon as he heard it the first time. Boy, are we going to miss the guys when they're all gone!
