Just my opinion but I would go with the stamping date model then add some days (get to that in a moment) rather than the projected date just because there is the chance that your projected date may be before some of the stamping dates found on your car. Been seen before.
Here is how I do it.
Giving some lead time for rail transportation across the country for many of the parts by comparing the stamping dates to the real build dates we have access to in 67 at San Jose around the same time as your car to take into account weather conditions and other possible situations that might occure annually. Yes there could be other things (work actions, rail routes that are better or worst that year,......) that could be different between the two years but IMHO its the best option with what we're given. Would be interested in how others would get a more likely correct guess - really
So for Chris and his specific question - do you have any specific dates? Lets say the easy ones
1- Any of the inner fender panels on the front of the car.
2- From sway bar mounting brackets
3- Rear bumper supports attached to the taillight panel and the trunk floors
4- What is the latest date you've found?
From there we'll see what the best guess (based on what you provide here or in a PM) might be for a date for you
