So Is It Riveted or Welded?

In the photos post #1
The hidden SO number has 2 leading numbers 55

55 12100054

The numbers are not on the fender tag but are in the vin tag.

I assume they are the vehicle type and engine or the like?

On my 67 dart convertible the leading numbers are 72.

7 could indicate convertible or 67 modle year. But the 2 has me confused, do you think they swapped the two digits and it should have been 27 (Convertible)?