I have recently come across this (not sure where - possibly a lecture I had from someone who used to work for QinetiQ (formerly the Royal Aircraft Establishment) or DSTL who did some work reproducing some of the experiments.
The tail was lifted by a crane to get the upkeep underneath.
B-50s (updated B-29s) had to be jacked up from the front (and one bomb bay door removed) to get a Mk.4 or Mk.6 Nuclear bomb into the bay. I will check what type of jack was used (begins with 'M'). The B-29s were manoeuvred over a pit with a lift for loading.