The cabinet numbers are: 200xxx and 200xxx. They were upgraded to 24/96 on 8/26/99. Both have the 24/96 seal. Firmware is 4.003.
Where are the electronics numbers?
With the 5k's, which are ported, the cabinet serial number is in the port and electronics are on the rear.
I don't know if 6ks are ported and if they are, if they are same place, but it’s a start.
If leading digit of cabinet is different (lower) than that of electronics, then thats an indicator that they have been upgraded - upgrade sticker may not be on every upgrade.
If 5k's, I would expect 18 bit upgraded to 96/24 to have cabinet (inside the port) as 1xxxxxx and electronics (on the back) as 2xxxxxxx (or later)