Michael Kramer wrote:
I've never seen any clear images of the LUT cranes in use, nor found any
specific info in Moonport. Were they used in routine stacking ops in some
way?

According to:

"http://www-pao.ksc.nasa.gov/kscpao/nasafact/count4fss.htm"

the hammerhead cranes provided "hoisting services as
required in pad operations". These service needs
were apparently infrequent enough for shuttle that it
was decided to remove the cranes in favor of use of
ground cranes when needed, simplifying maintenance.
I suspect that the hammerhead might have been used to
hoist the Saturn IB replacement fins during one of the
mid-1970s flights from LC 39.

- Ed Kyle