Hi dtwbcs . . .
You might start your research with this old thread:
Inliner's post circa Feb '07There is also the casting numbers page:
GMC Casting NumbersMilitary production can be tricky when compared to civilian. My 216 has a war surplus head. It carries a legible date but no casting number.
There is also a site that is specific to the duece-and-half trucks:
cckw.org regards,
stock49