The GMC CCKW

I just pressure washed the engine in my truck. Lo and behold there was an id block.
On it reads 270b7505b. On the other side is a data plate with the serial number 270 7505 and
data about bore and stroke etc. I am assuming the "b" stands for blank.

The block casting number is 2135412
The Head casting number is 6107142 / G242

From http://www.oldgmctrucks.com/Photos/GMC_Numbers.htm , I get:

The block is anything from a '46 - 54 and the head is from a '39 - '52 228

Beside the original data plate is another from the 229 Ordnance Depot rebuild. On it there is a date of 3 23 54.
There was a series of fire trucks converted in March of 45, which this one would fit into, so the 54 could be a transposed 45.

Is this a wartime engine or a post war rebuilt engine?

Neil

Looks to me like a post war block....but....that doesn't mean it's not a military engine
The depot rebuild tag dated '54 is just that..... the truck was rebuilt in '54
The way the Gov'ts contractors rebuild these or most vehicles is upon arrival the entire lot ( vehicles) is dismantled all the sub-assemblies are checked, rebuilt, or replaced,( ppossibly a new engine or transfer or.....)
The reassembly is like an assembly line and the components are brought up to keep the line going, irregardless of what vehicle the parts came from originally.
Also the "parts" ordered by Uncle Sam were an ongoing purchase and supply chain. ie: GMC didn't only build engines for the Gov't up to '45
Production continued untill the vehicles were phased out of use by the US
As well as several more parts were manufactured by European enterprizes ,given the continued use of the CCKW by our allies long after the war.
I have NOS gasket sets dated in the '70's to name only one
The same is true for all these "vintage" military vehicles

Hope this helps
John