Bread...
Which bellhousing are you running? 1939, or 1954?
Obviously the 1939 bh has a provisions for the brake and clutch pedal, while the 1954 bh does not.
For my 1940 gmc, I used the 1940 bell housing, same as 1939-1947, an adapter plate for the transmission( NV4500), and the brake and clutch pedals off a 1.5 ton 1946 gmc truck. Many gm trucks of the era used a frame mounted master cylinder. The brake pedal would pull a linkage rod forward towards the front of the vehicle. This rod was connected to a lever on the frame. The frame lever had another rod that went from it to a Master cylinder. The push rod for the MC faced rearward, so when you steped on the brake, it pulled the linkage rod and lever forward, causing the additional rod to push the MC.
This sounds complicated, but the implication is that you can use a generic frame mount mc.
This picture from the parts catalog shows most of the pieces.
http://chevy.oldcarmanualproject.com/1929_54chevyparts/04/295.HTM
