Hi Thirlwell,
Was looking though some of the stuff on
Old Online Chevy Manuals and all I could find were references to 216 engines in the 1951 trucks.
Look in the links section of Stovebolt. Might be something there.
As fab51 mentioned, I recall reading somewhere that the 235 was an option for some models. If you post the engine serial number which is located just behind the distributor, someone here can tell you if it is for your model year.
The serial number should begin with something like JBA JBM BJCA BJCM JCD JCQ JAD JDA JEA or JEM.
Now waiting for the 1948 - 1951 Truck Shop Manual to arrive in the mail. Will check that hopefully soon.