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.

"Nothing astonishes men so much as common sense and plain dealing." - Ralph Waldo Emerson