The back board goes together very similar to the front board, except that it doesn't have Delrin nuts or a motor mount plate.
The bearing block is the same as the one for the front board, check the center bore to make sure you put the larger recess that holds the bearing for the leadscrew outward from the board. The bearing block doesn't have a motor plate backing it up on the far side of the back board, so there'll be washers that sit under the heads of the machine screws, as in the image above (click either image to enlarge.) It doesn't matter which way you install the screws, so far as I can tell--heads in or heads out, it don't make no nevermind.
Shaft End Mounts
The shaft mounts are also the same as the front board. A machine screw slips into the open end and through the bottom. Put the screw through the holes on each side of the bearing block. A washer and nut goes on the other side. They should be secured no more than finger-tight, not at all tight. When we're adjusting the machine you'll need to be able to turn these.