I am hoping Ted can respond to this.  I was cleaning up some parts and noticed that there are three distinctively different cup washers that retain the intake manifold to the heads.  I notice that one is totally dome shaped while another seems to be of less material, and has a flatter area where the stud goes through the part.  The  third variation is about halfway between the two.  There may be more.  Are any of these significant?  Is there a certain year when they were changed?  Thanks