I have a 56 block with what I assume is an aftermarket adapter.  It has the thin base plate on the block with the slots on the top that is OEM ( I think), then a hard plastic ( rubber?) stepped washer, then the thick outer plate.  I assume fiber gasket on the block, then thin plate, then plastic washer, then thick plate ( with the three holes on the top side).  This is the way it was when I took it off, don't know if it leaked or not.
  I have 3 of the chrome acorn nut for the t-bird valve covers, missing 1.  Anybody have a good source?

Thanks
Paul