Sounds like you have missed the elevator (in Martens Bluff to/from Lower Martens bluff). That is where the dummy is (lever around the corner) and the idol out the single door (not heading out of the compound, once you come up the elevator).You should find random bits of paper that have numbers on them (on dead trang) or you can swipe them, I think. Otherwise the combination is something I forgot, but includes the number 7, 4, and 0 ... maybe a 1.
Tools for Wizardry(r) 7