Be aware, that part numbers don't always "tell the tale", but illustrations CAN. For example, if there are two identical items, initially, but for one year, it needs an extra hole drilled in the metal, that generates a different part number from the original item, although one is backward compatible. But we don't know this just from the numbers, unless they supercede the part number to the newer one from the older one. If it's due to "vents", there are three part numbers of tanks for the '67-'73 cars, related to "no vents" to "2 vents" or "4 vents". We know that the sending units all work, back to about '65 or earlier. And capacity ratings are very similar. The other thing is that if a supplier/vendor (where Chrysler got the item from) might change, that can generate a different part number, too, for an item built to the exact same specs.
Also, in order for these publications to go to print and be delivered to the dealerships just prior to the vehicles arriving, they had to be finalized in later July of the year. If there were any significant production changes, from the initial printing, they would be noted in later TSBs or Dealer Letters, or a "later-in-the-production year" parts book, possibly.
Filler neck hole locations can be an issue, though.
I'll concur that the '66 and '67 Chrysler tanks look to be the same thing, from a casual look at things. Why I was wondering if there was something specific in how it indexed with the floorpan of the trunk, different spacing of the hold-down straps, or a slightly different contour to go with the way the rear quarter panels angle from the rear wheels to the rear bumper?
CBODY67