400sb head-piston clearence

  So i built this 400sb... and i was fairly certain there was enough clearence between the heads and the pistons... i guess i was wrong, it sounds like a train running under the hood.... so they dont make shims for that motor and i spent 600% on the pistons so i cant redo anything... has any one ever gotten away with doubling up on headgaskets? and if so then did you use any kind of sealent between them?
 
 
  Thanks