KingG - The original master cylinder for your '49 4400 was GM# 5454382 - 1-1/4" diameter cylinder bore that fit 1947-51 3/4 ton through 2 ton trucks. 1/2 ton truck master cylinders are not correct for your truck.
You can find the one you need available from several of our regular well known vendors, like
The Filling Station FS-241A or from various FLAPS under Dorman# M9220.
Even rockauto.com carries them as
Dorman M9220. BTW - rockauto is the best priced unit I found, but doesn't include shipping and tax which will up that cost just a bit.
Hope this helps.
