I have a 70 SS. Under the PNT and Interior code there is the build date code (10D) and some other numbers on the same row as the build date. I heard it was something to do at the body plant but not sure. Can anyone help tell me what the third row of numbers mean on the cowl tag.

Its a plant code called the DP Sequence Number. It was just a Data Processing generated number, used for keeping track of the car in the computer system.

Either the complete number (about 12 digits) or a truncated portion was on the Body Tag. The complete number was found in Box 24 on the build sheet.

Almost each plant was unique in what numbers from block 24, and block 10 in two plants, they used on the body plate.

Atlanta & Van Nuys:
First group of 6 are found in block 24. The first 2 of the second group of six are found in block 10 (under SCHED) and the last four are found in block 24.

Arlington put 3 digits immediately after the body date.

Baltimore put 4 digits under the paint code.

Flint put no extra digits on the body plate at all.

Kansas City put 5 digits one space after the body date.

Go figure...