One of the interesting things about this truck is that there was the remains of a box left on the back.  After some research, I have settled on this box being a Martin-Parry box.  Here is a link with some information on the box  https://www.martin-parry.com/

I think this is a Grain-Stock Express Body.  Although I am not sure on that.  Here is an example from a dealer’s catolog.

The cab on this truck is an original International SA cab that is listed in the Six Speed Special parts manual.  Next is a group of photos of what is left of my box.