I found this yesterday in the booklet of AC/DC's Live at Donington DVD, looks like Cliff Williams had an Alembic pickup in his P bass:
(http://club.alembicguitars.net/Images/449/197715.jpg)
Alembic and Mesa monstrous combination
I must have heard/seen this bass irl, Monsters of rock '91 was the first arena show I've attended (AC/DC, 'tallica, Queensryche and Black crowes in Nijmegen sept 1)
Good eyes to spot. I wonder if he played with active or passive electronics in that bass.