[mleder]

Would you happen to have a different lower plate that you can swap out for a test run?. When the plate goes bad the tab on the bottom will show continuity to the main part of the plate. The insulating washers that the rivits pass thru may be old or on the intermitant part of being good/bad.When pressure from the ingnition cable or even reassembly into the distributor body or vibration from engine running might possibily cause the the plate to go to ground. This condition may only happen possibly when you've gotten everything togather. This could disapear when you remove part of the assembly or move it to the bench for inspection and testing. You would not be able to determine by a visual check of the rivits or washers if this odd thing were happening. A long shot but one more thing to consider.