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As you have to lift a heavy weight, then watch how you design to attach structure to the steel-cable slings. It should be very safe (oversized if you like it) but it does not mean that it might take a long time to release the structure once it is on its place.
No man should be struggling with such heavy elements (whatever you designed for attachments) "in the air", despite the use of security belts, a net, a life-guard steel cable and the like.
Preliminary sketch
Photo: lifting a 30 metric tons beam (preassembled with cross-beams), l=47 meters. Teatro Argentino de La Plata - Buenos Aires, Argentina.
Note that the red painted plates and pin used to lift this beam were the same used for all the different beams in the whole erection. Of course they are heavy, but once they are loosen up, the crane will take them away, not the workers.
Also we thought that it was better to have only one pin than several bolts to unscrew, as bolts usually get stucked.
For this beam you can see in this mpeg:
A) It was used a tensioned steel cable to prestress the lower bars of the stand-alone beam (it is parallel at both sides of the lower side, at the ends of the cross-beams). This is because it was verified before that it could not resist lateral buckling of the lower side.
B) Beams are lifted with their supports already bolted at both ends. You should always try to redesign anchorages that do not allow you to do so.
C) The concrete walls had to be partially removed because interferred with the beams. (Always check probable project errors and correct them before you start the operation).
D) Other ropes are used to guide the beam into place and to have it under control. These are slow operations. Do not hurry up to anyone involved on it. Always take your time.
Another stand alone truss-beam (a big cantilevered one) of a hangar.
Photo: Hangar AA in Aeroparque Newbery, Buenos Aires. Puting into place a 40m cantilever beam. To release fast the two cranes, the frame will be left hanging from the steel tower in the front side while it is being bolted to the building 's side.