Well, they are likely to be different in the deco trucks. Most larger trucks had the Master Cylinder mounted on the frame. Most 1/2 tons had the MC mounted in a cradle that bolted to the transmission and the bellhousing. Sure in both trucks the pedals bolted to the bellhousing, but how they actually worked was completly different.

On my 1940 GMC 3/4 ton, I had the cradle type bracket for the MC. I figured it would be eazier to put a dual chamber MC with the other setup because I was putting a larger transmission in. I found a set on ebay and rebuilt them. As for the actual length of the clutch pedals... I don't know, but I believe it does have a different pivot point with relation to the bellhousing. I can email you pics of both setups which are on the shelf.

John