I finally had time to pull the head - took it to Mark at DeGoff's Cylinder Head Service in Northridge, and he pronounced it terminally cracked; unrepairable. Took him about 15 seconds to find the "Grand Canyon" crack, and its little buddies. Two combustion chambers look like the surface of the moon. I guess I will look for a used engine - this condition had obviously been developing for a long time, and given the elevated level of tin reported by the oil lab, I just don't trust the bottom end. Worst car I've ever bought - a very expensive lesson. Thanks again for all the tips. The news was bad, but Mark really knows his stuff. BigMac