yes an assembly line worker could have corrected a jumbled stamp, but i wouldnt think that to be likely

many things are possible,
and there are usually exceptions to the way things were done

ive only seen short or long blocks being warrentied,

only shortblocks show up in the parts book (at least the 1969 book)

i honestly dont know if a complete motor was available

i do have a flier from chrysler to a dealer from when the 1965 hemi engines were being sold off as complete units

but i think that was only because it was a race type motor,
not sure if otherwise

do you have pics of the tag on the motor?