If anyone's still interested, I ended up finding the round disc inside the
air filter box, the outer half of the rectangular part in the air intake
distributor, and the now destroyed spring/pin inside of #4 cylinder. It
had started making noise as it was slammed between the head and piston
end. Luckily, it didn't make it into the rings, and the cylinder walls
weren't scored. Thank god. It was a long Saturday, but we got the engine
out, torn down, reassembled, back in and running all in one day.