Hi Brian, a pretty good description of a giant squid apart from the 2 heads. There's a great 16th century broadside with sketch of one such on the EBBA website, but this one was washed ashore off the Dutch coast.

Yes, few ballads. Considering the reality of sea monsters found you would have thought that this would have provoked lots of folklore and ballads, but the only ones that seem to have survived are the more recent comic ones. Whales of course have been known and hunted since the advent of print so seafarers would have been familiar with them, and sightings of giant squid are pretty rare. The supernatural in ballads seems to have been confined to ghosts, fairies, giants, witches and the like.