Cant find that part number. Cant even find diagrams of any AAR / A12 / Shaker stuff in any of my parts books.

Don't know if this is what your looking for, P/N 3418658 is for sale on ebay right now. Paul

should be 3412056 according to the parts book.

On one of my A12 bases...

As stated 3412056 is the correct part number for an A12 seal.
3418658 is the part number used for the adapter ring seal used in a shaker assembly.
In the case of the one pictured above it could have been and likely was the aforementioned shaker seal cut to length ,
re-glued, and used on the A12 base, since the shaker seal is longer.
The other possibility could be it was mis-stamped but I've never seen them stamped that close to were they are joined.

Saw this online....
"Of course, the most noticeable item was the black fiberglass lift-off hood, which carried the Chrysler part number 3412056 and was held in place with four racing-style pins"

Parts books are confusing with A12 parts and and 3412056 shows up twice,
once as the Superbee liftoff hood itself in 15-03-3, the roadrunner hood being part number 3412055.
It also shows up in 15-03-64.
I am not so sure now on checking, which is the actual A12 seal number, if in fact it even had one.
I know you could buy the A12 air cleaner assembly, that is base with seal installed and lid, all under part number 3412058