how many 57 chevy sedan delivery cars with side windows were made?

I had some documentation, but lost all the original paperwork in a house fire. I know it belonged to the government until 1968 & has been in our family for decades (I got it from my father-in-law when he passed). It has a V-8 w/a 3speed+overdrive. original hounds tooth bucket seats and only a drivers side sun visor. What makes it different is that it has long side glass instead of the steel sign panel sides and a one piece rear door instead of a tail gate. Any accurate info on this car would be appreciated.