The Back is in the Bigger cabinet! Well I got the back installed in the cabinet and got it stained as well. I took a sheet of Luan and cut it too fit the back of the cabinet. I then used spacers too keep the rails and bottoms the right distance apart. I marked the back where the bottoms and rails are and used these lines too install 1inch sheet rock screws thru the back and into all the rails and bottoms. Use as many as you think needed too keep them from sagging.
The pictures will give you an idea of the actual spacing and how the pipes set in the rack. As you can see there is plenty of room for longer pipes and even the shorter ones and bent ones fit very well. There is also plenty of room for a lot larger bowl pipes.
There are only 43 pipes in the rack in the picture. This will give you an idea of how it will look full.