The S-92 does not have to be leveled for a main gearbox change. If the aircraft is on a surface with more than 10-15 degrees of slope you may have trouble getting the gearbox in place.
The job can be done with a crane, just put a chain hoist on the hook and make the fine adjustments by hand. I've worked with some crane operators that are smoother than a hangar hoist and some that are a hazard.
Any job that will take a couple of days would preferably be done in a hangar. Some customers mandate that jobs like this be done in a hangar.