66 67 12 bolts

I have a chance to buy a 66 Nova 12 bolt to go under my recently acquired Nova and the seller also has a 67 Nova 12 bolt. The stamp numbers are on top of the axle, unlike Camaros which are stamped in the 3' O clock position and they look not to be gang stamped almost crooked. My questions; is that the way they were stamped and also the 66 has a casting number 385280n and the 67 has a casting number 3894860nf are these correct with two different numbers? Any help would be appreciated from some of you Nova experts.
Thanks