I put 2 x 2's across the 2 x 6 joists to keep them straight. Then we flipped the top over and bolted on the posts. Now the Pergola is like a giant table. We made sure the legs were square both ways with the top. We dragged the pergola back a few feet and flipped it over. The heavy posts made it easy to flip over. It went right down into to the holes as planned and nobody got hurt. It took 6 of us to get it up. Then we went around and leveled the posts. Now we are ready to dump concrete in the post holes.
This is what the underneath side looks like.