You should be able to determine if the cab is '47 or '48 from the engine compartment as well as inside. The mast hole had to be vertically elongated to accommodate the column shifter in '48.
Also if the doorpost ID plate exists, '47 serial numbers begin with EP, ER and ES. 1948 serial numbers begin with FP, FR and FS.
RdsLessTaken/Don

This '47 mast hole is like Brad Allens.
http://i1291.photobucket.com/albums/b542/RdLessTaken/RdLessTaken%20Trucks/IMG_79043_zpse102079b.jpg