Spendy '71 340 Exhaust Manifolds (Craigslist Ad)

NOS does not mean perfect condition,new in the box.New old stock could have been in a damp warehouse and rusting away or have shelf war from handling and still be new old stock.And nos does not mean factory original,merely a run of replacement parts from some manufacturer and may indeed differ from the original factory piece somewhat.
..I have bought nos parts that were not used and were not nice pieces at all.
"623 is correct for passenger side 340.