Interesting...according to GMC Paul's decoder [
http://www.gmcpauls.com/67-72_gmc.htm] your truck is as follows:
C= 2wd
E= V8 gas
1= 1/2 ton
OD= wideside (fleetside bed)
P= Pontiac, Mi. ass'y plant
B= 1968
everything else= serial #
if it is indeed a '68, the 327 could be stock. if it is a '70, i don't think 327's were any longer an option.