Here is a link to the page where I try to describe how I put a dual master cylinder into my 1940.

http://home.twcny.rr.com/schickling/1940Chevy/rebuild5.html

I also have a T-5 transmission so you don't need the special bell housing if you retain your original transmission.

Is this the same setup as the 38?

Bill Schickling

1940 1/2 ton, 1940 3/4 ton
My web page