You might want to look at the 1938 Specifications Manual (maybe you have) and determine what model size truck you have.

The wheel base would be a good piece of identification information?
http://chevy.oldcarmanualproject.com/chevyresto/38index.htm

Do you have a Vehicle Serial Number?
http://chevy.oldcarmanualproject.com/chevyresto/38index.htm
http://chevy.oldcarmanualproject.com/chevyresto/3804.htm