Well, if you look at post #9 of the following thread, you can see me flipping my frame using the gantries that were built to lift the shell and 3 chain hoists.
The way I did it, is I used a loop of high strength webbing inside the A-frame and attached it to a single chain hoist. The way this worked, the hook of the hoist could slip around the circumfrence of the loop as the frame rotated 180 degress, thus, I didn't have to create any fance pivot, and there was very little chance that my hoist could lose its connection with that end of the frame.
On the rear end of the frame, I used two hoists that had a common anchor at the center of the gantry cross beam. They were each connected to the far corner of the frame, again with chain or webbing attached inside the rear cross member so that they could not slip off and allow the frame to drop.
To lift and flip, I essentially lifted the entire frame up to a level of about 4 ft off the ground, and then I started to raise one of the rear corners, while slacking off on the other to execture an control the rotation. Once the fram was hanging vertically (ie., entirely from one of the hoists), I would disconnect the lowermost hoist, flip it around to the other side, and then reverse the process until the frame was horizontal again, but upside down.