Mickey - It took me a little bit to remember where I saw the decoding details to help you answer your question, but here you go!
The pics snapped below from 1983 and 1984 Chevy Parts books shows your info decodes as follows:
KAS = 1978 or 79 - C10 - 8.875 carrier with 3.07 gear set, Standard carrier (non-Posi)
137 = 137th day of the calendar year (no idea how to tell which year?)
W = Warren plant
87 = Shift code
As far as I can figure, this is correct. Others with more knowledge of the 12-Bolts may have more details. Hope this is helpful.
