SN30520 was up for sale on eBay and got as high a bid as $2,557.07 on June 23, 2005 but that was insufficiently high enough to meet the seller's reserve so the unit did not sell.
This unit is fully playable and the owner describes a copper oval plate is mounted on the back that says 375. The owner is not certain what this number means (the 375th 2-player machine built?) and no other machines on my site have a similar plate on them so I am at a loss to explain it either.