Not sure where the dart is - on the b body there is one stamped in the core support - far right above the rad opening ( when standing at the front of the car ) on the vertical face and there is one under the backlight under the package tray cardboard - passenger side parallel to the backlight.
What year B-body are you referring to?
I was always under the impression it started with the '68 model year??????? If it started before that then it would have been for internal identification in the BIW and paint departments I would think?
