Possible 1972 Six Pack carburetors + odd date on 1970 carb

.
Help identifying possible 1972 Six Pack outboard carburetors.
.
.
I recently purchased a complete Six Pack set-up and a separate pair of carburetors from a local hot rod shop.
The complete set-up was installed on a small block 1970-72 Plymouth Duster at the time of purchase. That complete set-up consisted of a mash-up of parts, but was all good stuff...it used an original 1970 aluminum intake manifold, original 1969 A12 air cleaner assembly steel base with a reproduction thick fiberglass lid and used two (original?) air filters stacked on top of each other to properly mate it to the aftermarket Six Pack lift off hood the car had on it.
The other set of carbs. were "loose" and just mounted to a one-piece 1" thick billet aluminum Six Pack carb spacer for the sake of easy organization, I assume.
I needed a good air cleaner assembly for my A12 Super Bee 4-speed, so I worked out a deal for everything mentioned...$3,000 cash. I was very happy and excited.
.
That being said, I do have a couple questions about my acquisition...
.
.
One of the center carbs. is a 1970 4-speed carb. with a correct List - 4375, however it has a date of 0819.
Why is the date so early on this carb.?
.
.
Here is where things become interesting...or at least I hope...
.
.
The two outboards were list numbers I have never heard of before. I had just assumed they were GM or Ford pieces, but now I believe they could possibly be for the nearly non-existent 1972 440 Six Pack cars.

List - 6405, date 1411
List - 6406, date 1411
.
They are clearly a matched set, wherever they are from.
Anyone know if these are ultra rare 1972 Six Pack carbs.or if they are for something much less exciting (to me anyways)?!?

See this post.

https://board.moparts.org/ubbthreads/ubbt...1972-440-6.html


Dates will be off cause those carbs were not used in normal production.

Get ahold of Bob K, or Paul P...

Thanks John!

Oddly enough that is the intake and carburetors that I purchased.

Small world.

I "know" the original poster of that link.

I sold Paul P. a set of Six Pack carbs. a couple years ago...I didn't even think to contact him or Bob K, both are local.

Thanks again.

6405 & 6406 numbered carburetors are listed in the Holley Illustrated Parts & Specs Manuel, as 1972 Chrysler 440 Eng. Spec. 3 X 2 BBL. Front Std. & Auto. Trans. Calif.
So those numbers did have an application from the get go, in the beginning.

Thanks for the information, everyone.