I mentioned in my last post that I was planning to use a jig to align the corbel ring properly around the tower. Plans are changing on the fly. The idea was to make a stop collar to slip over the larger diamter of the tower and use it to seat the corbel ring down. But in light of the fact that there is a lot going on with the roof of this machicolation, I think it could become the stop ring and the corbel ring with its wall could be slipped up and against it later. That means that the roof would be glued in position first along with its chimneys, turret and dormers.
In this shot, you can see the roof ring below the tower (sample from another tower yet to be built) and a brown cardboard washer. The washer was added to the upper walls of the machicolation...