The axle plans showing brakes and related parts is one of those places on the plans where the order and orientation in which the parts go looks pretty mysterious in the beginning.
I have to admit I also had to lookup pictures from other builders in order to find the correct order and orientation of the parts.

The brake mount flange in steel is the center piece which holds an aluminum support bracket for the inside of the fibreglass wheel pants.
This bracket is spaced away from the brake caliper by some spacers which I first made using a tube cutter and grinding it down on sandpaper in the drill press.

You split the brake cylinder in 2 halves by unthightening the bolts holding the parts together.

Then you slide the inside part on the brake mount flange.

When you slide the other part back in place. You will notice that the wheelpant support bracket is in the way and needs some customizing.

 Close up view with a marked circle that should be removed.

In the bottom image, the flange was adjusted and the brake caliper can now be installed and move without interference.