Using Tom's explanation of your L138 date code you have a Dec 13, 1968 engine built for the 69' models.
Looking at this list from chuckthetruck,
http://no25.chuckthetruck.com/page3.html the 'PC' engine serial number suffix shows up as a 250 with manual transmission for trucks in 1969.
The date code and the 'PC' suffix says 250 engine in my thinking.
Hope this helps.