FW340P31770423;
F - Series (model year) 1970
W - Windsor, Ontario engine assembly plant
340 - 340 cid
P - Premium fuel required
3177 - Final assembly date from the 10,000 day calendar - April 9, 1970
0423 - 423rd engine assembled at this plant on the date above.
The 1970 TSB that covers the engine markings does not mention a "K" at all. You can read it at this link if you like -
http://www.hamtramck-historical.com/1970-Dodge-TSB-Index.shtml Drop down to Chapter 25 in the grid & read D70-25-1, there are 8 pages.