I know this is old Tom but, were you around for the land move? How did they raise the Drum up so high? Did they close and fill the cofferdam with sand to float her up high enough to settle on it and then drain the water and add the chocks? That's what the picks "look like" but I am just guessing.
Edit: On further review it looks like the sand they dug out, they put back in. This would put the ground level back to about where it was before the channel was dug and the Drum would float higher with the sand added adding to the water's height in the coffer. The one picture shows most of the dirt/sand in the center of the Drum This would allow the bow to be dug/chocked first to stablize any "bow down" attitude. I guess then you work your way back.