The frame comes already assembled and square. 

The scribed squares are the step hatches.  These should be hinged at the observation end, at the buffer.  The 5 buffer pieces are of 2 types: 2 squarish and 3 rounded. The 3 rounded go on the observation end stacked 3 high and the bottom of the buffer is even with bottom of frame. (Center sills drop lower.) The 2 squarish buffers are for the vestibule end. Again, 2 high and even with the bottom of the frame.

In the above picture, the observation end is closest to the viewer.  Note that the pair of round holes in the centersill are towards the vestibule end.

You will have to assemble the steps and the battery box.

For the battery box, there are 7 pieces. In 1/8" poplar, you get 2 ends (with notches), a bottom, a top and a back all with tabs. The front of the box has 2 ea 1/16" birch pieces, one 3/8" for the top (this will drop the door to below the side beam) and the 1-1/8" door. (You also get 2 hinges, one handle and a bunch of little nails for them. And one #72 drill bit.)

On the steps, there are 8 pieces. 2 notched sides that the steps and kick plates fit into. 2 plain sides to cover the notches. 2 steps that are identical, 1 lower kick plate, and 1 upper kick plate. The upper kick plate is smaller that the lower kick plate and both kick plates are smaller than the steps.

The picture above shows one possible arrangement of the tanks and other details. Every car was done differently, but this should help for placement.  Note that the observation end is to the left, the vestibule end to the right.

Plumbing:

You can use 3/32 rod to represent 2 inch pipe for the train air line and the steam line and then 1/16 inch to represent 1 inch pipe for the water lines and the sub runs off the main for both steam and air.  Check out the fishing tackle section of your hardware store:  Red Wolf #6 hooks to be an inexpensive ource of eyes for 1/16 rod.  For 3/32...

In general terms, on the far side of the picture is the passenger air brake system; at the right end in the middle attached to the centresill is a 5 kw generator belt driven from a truck axle; on the near side in the picture from left to right are gas tanks for the buffet, the main water tank and the pressurized tank and then the battery box. There are a pair of steam regulators at the left end of the car. The battery box is not yet completed and is just sitting loose.

A more detailed shot of the brake system with its characteristic tanks and big universal control valve near the lower left.