Malikasal:
More info on the truss would be helpful in making the final determination on how to lift it. What weight, radius, depth, actually all the details of the truss make-up. If it is a fairly light truss, you might be worried about it buckling under the secondary lifting forces. In which case you might need a spreader beam. In any case you have to pay attention to the stresses in the truss caused by the lift, they are much different than what was originally designed for. The boom height and sling lengths must be considered so that the lift does not impart to large a concentrated axial load in the top chord at a couple panel points. I would probably lift the truss from three points. The two primary pick points would be far enough apart so that the curved side at the center of the truss was heavier by some significant amount than the two ends. That is, the truss would tend to tip to that side if only the two pick points were used. Then, the third pick point is with an adjustable length sling and down to the center of the truss. While you want to lift the truss essentially in a vertical orientation, you want it leaning and loading that third sling, so it can not roll toward the two ends. Remember, that the truss and rigging will always swing and roll so that the C.G. of the entire system is directly under the hook. Maybe four pick points, with two spreader beams above the truss would be a better solution. Then you adjust the pick points on the two spreader beams to cause the balance. Study your truss and lifting system in plan view and in end view, with the crane hook above as your final lifting point and you should be able to work out the geometry of the system.
