There are a couple differences in small items. If the truck has a floor mounted parking brake the hardware for the foot operated brake will need to be sourced, up to and including the firewall mounting bracket. If the truck has a 2-speed rear end there will be some additional hardware and holes on the firewall to consider. Dimensionally they are the same, mounts changed in 1949 to frame shackles from a center pivot and bumpers. Trucks in the U.S. are rated to 2-tons usually but in other markets can be equipped for ratings as high as 5-tons. All my comments are for AD's. Your best bet is to find a similar year cab so the changeover shares common parts, 47-48 or 49-53 or 54-55 1st Series.
http://www.flickr.com/photos/advance-design_parts_co/9527752160/in/set-72157631872034068