I've stepped a mast of that length (but much lighter, about 40kg), using a single spar, mounted vertically just to one side of the partners, and stayed with three or four stays to cleats and other strong deck fittings. The mast was laid on deck, heel forward. It took one person to hoist the mast using a tackle, one person to guide the heel and one person to adjust the stays (with great care) so that the mast was vertically above the partners. Obviously, with both a single spar and an A frame, they must be long enough that the tackle has plenty of drift so that the mast does not contact the spar(s).
A catamaran in Ravenglass harbour has a high wingmast, and sheer legs are used to lower it. They are made from large diameter aluminium tube, and the owner says that he almost needs sheer legs to hoist the sheer legs, they are so heavy.
Unless the operation is to be carried out frequently, so that you stay in practice with the methods of handling heavy equipment safely, it might be better to engage a crane to do the job.