See pages 29-31 of RPCyc Volume 10 by Pat Wider for excellent illustrations.

With the exception of one 1936 order that had an Ajax hand brake (82500-84749, built in Laurel), the NP used the "Miner Ideal Safety Hand Brake" staff-type brakes on its stock cars built in the 1930's (as modeled by Jack Parker and Central Valley).  

Illustrations and rosters of the stock cars, brakes and other features can be found in two articles in The Mainstreeter, Volume 6 #2, 1987

• The NP's Stock Cars
• Hauling Stock on the NP

A searchable bibliography of The Mainstreeter can be found here
http://www.nprha.org/lists/np%20bibliography/mainstreeter%20view.aspx?view=%7B9829da62%2D55a1%2D41e0%2D99ff%2Dfcdf07ab39e6%7D&showingrid=html

Diagrams can be found here
http://www.nprha.org/NP%20Stock%20Cars/Forms/Thumbnails.aspx

Tim O'Connor, writing to the old yahoo group,

Rufus Cone
Bozeman, MT