340 k frame
There's a few threads with pictures of the 340 K frames. The reinforcements were minimal and usually pretty poorly done. They started in '70 and ran through '72 for sure, seems like '73 had them as well but they stopped before '74.
The difference is literally a washer (that does nothing) and a couple of half moon washer shapes welded to the LCA pivot tube holes. You could do a better job of reinforcing the LCA pivot tubes with a couple of heavy duty washers from the hardware store welded on with a Harbor Freight MIG welder, even if you don't really know how to weld. Nothing else was different about the K's, and some of the factory welds on that stuff were atrocious.
This is the washer, used to ID the K's
These are the LCA pivot "reinforcements". And the "reinforcement" term is used very loosely.
More info here
340 K Member ??