that last K frame bolt...

[eldubb440]

In the A body cars that I have cut up, there is a stamped steel "bracket" that lays over the top of that threaded nut. It is welded to the frame rail, not the nut. I would think that they did some if not all B body cars the same way. I don't recall the year or model of your car though.
Yours is still a good idea. SCORE !

this one is a 70..... I didn't drill a big enough hole to look, but I kind of remembered from another one I was into...… I don't even think it's a nut as we know it (hex) …… I believe it is round, and a bit on the tall side; maybe 3/4 inch

 

[Kern Dog]

WEll, I'm not cutting into my car to prove either of us right!