VIN.
There isn't one on the frame. The only numbers I could ever find on the frame were date codes. No VIN. No Partial VIN. No serial number. I don't even think I found a body code.
The official body tag is either on the dash or the door, but you knew that.
There IS a serialized tag under the fenders on the body at the cowl, but you have to remove the front clip to see it. If you are planning on doing a fill-body restoration, then you'll see it.
Here is where it was located on my 1970 Mercury:

- Location of serialized body tag

- Closeup of Body tag under fenders.
The number will be the first two digits of the VIN (Year and Factory Code) and then the 6-digit serial number.