In thinking of the size and weight of nuclear weapons, don't forget that Britain's Royal Artillery - among others - had 8" Howitzers that fired a tactical nuclear shell, in about the same period. I cannot remember what it weighed, but sure as hell it was only 8" diameter.
The 5.5" shells of the 3 5.5s I was in charge of weighed 80lbs (and could be delivered over 18,000 yards range), but the nuclear shell may have had a higher weight per unit of volume.
In any case, I'm sure a Gannet could have carried one, although in a self-immolating mission.