I just went out to check my 49 Dodge. There is a "body number" on a plate attached to the firewall, but the "Vehicle Number" is on a plate attached to the drivers' side door jamb. This number is the "Identification Number" on my title.
I do have a vague memory that way back, some states used the engine number as the vehicle identification number, but I don't think any of them have done that in the past 75 years or so.