Since nobody else has spoken up, here is my two cents worth. Unless you want to spend money narrowing a rearend, start with a proven swap. There is a ton of information on the net, magazines, and books. Most companies that sell the rear dual leaf spring kit can suggest a rearend. For the 40 Ford, the most common is the Granada , Bronco, or 57-59 Ford rearend. I went with the Bronco unit in my 37 Ford to keep the 5 x 5 1/2 bolt pattern. Here are a couple of links to some info on Ford 9".

http://www.carnut.com/specs/frear.html

http://www.clubfte.com/users/jniolon...rentialid.html

http://www.kevinstang.com/Ninecase.htm

Comments Anybody else?

Mark