Guess that bolt ....new game

cosgig said
There are 2 different sizes....5/16" and 3/8"!! I believe that the smaller 5/16" are 68 and earlier!! Geof

They were still using the one pictured on 75 Duster. I'm sure changes were phased in, probably starting with easiest/ least obvious first. So something like this may have been officially for a 70, but they could have made the switch sometime in 69.