Here are my 2 67 rear dates (plus engines):
NOR 5B - 396/MT/3:31 posi - date - 0331 - This is the performance rear option. Lag about 6 weeks. (engine date 0308)
LOS 4B - 396/AT/3:07 non-posi - date - 0404 - This is the standard rear for this base engine option. Lag about 9 days. (engine date 0214 - assembled with love
I think the gear ratio installed may have an effect on the assembly date of the rear vs. the car.
The standard ratios should have less of a date lag because they would be used on all cars that didn't have the optional rear ordered, as is the case of my LOS car.