Um...again, have a look at the following link:
It shows how the two gantries are used to lift a shell, as well as for frame work.
In the spirit of offering "professional" advice, within the above linked thread (toward the end) is some discussion about bracing, from a forums member who actually gets paid to do rennovations. His take, my experience, and many others' is that bracing is not needed when lifting the shell from above. This is the beauty of using the gantries--yes you will spend some time and money building them, but you will save time and money by not fussing with interior bracing to jack against.