Oh, many thanks for all that- that is all useful BUT I still have a question! Why is the tape measure of having the piston all the way down perfectly, using a level for the corresponding piston to be all the way UP, inadequate. It is 3 and 7/8 inches at MOST and that is just too far off the requirement of 3.98 inches that even if we were off a little, it is not close enough to feel right about. Does that seem reasonable? That we could squeeze another 1/8 inch? And what about ANOTHER suggestion, that the pistons should have a marking on them that shows they are bored .003 over. THEN another guy said the 6cME is a Mercury Replacement Engine?? Oh, and the last time I got under that car, it is on a horrid driveway on a building site, the weeds in my hair were so frightful my son blew me off with an air compressor and it was equally horrid. He is an engineering student at Seattle U and thinks he knows everything, but I am finding that he is way over confident this thing IS a 390.Too many brains!