That number is the model designation. Found this picture in your build:
If you follow your link, you'll see that all C20 Cab and Chassis from 67-72 use that Model Designation.
Looking at your VIN: CCE232J170359
And using LMC's Catalog Decoder:
http://www.lmctruck.com/icatalog/cb/full.aspx?Page=9
We Get:
C - Chevrolet
C - 2 Wheel Drive
E - 8 Cyl
2 - 3/4 ton
3 - Cab & Chassis (Not listed on LMC, Found Elsewhere)
2- 1972
J - Janesville
170359 - Vehicle Number