So there have been a few people around here who want to know how to geomerge the crane http://www.youtube.com/watch?v=WbsJ0TMFp_s This is the tutorial, hope it helps :halo forge discussion:
Geomerging using an interlock is actually more precise than using doors. I almost always geomerge with interlocks rather than doors when I want absolutely perfect symmetry. Another bonus in my experience is that things are less likely to fall through the floor when using interlocked boxes rather than doors. That could just be coincidence though.