Hi dtwbcs . . .

You might start your research with this old thread:
Inliner's post circa Feb '07

There is also the casting numbers page:
GMC Casting Numbers

Military 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