Just to make sure that we are all thinking the same thing:
The lower control arm is held to the K member by the pivot shaft. That pivot shaft is held into the LCA by being pressed into the bushing. The K member has a hole approximately 3/4" in diameter that the pivot shaft passes through. At the front, a fine threaded nut and a flat washer hold the assembly together. The K member uses no bushing. It is a metal to metal connection. THIS is fine as long as the bushings are okay. If the bushing rubber fails and falls out, the lower control arm will start to move around. That movement stresses the welded 3/4" tube and soon thereafter, the welds break. After enough time, the hole stretches or tears the K member. For future reference, if the toe and camber suddenly change, check the LCA bushings right away.
Did I understand that you currently have a slant six in the car? Slanty k members aren't that difficult to find, but the problem is, I doubt that guys are bringing them to swap meets to sell. Most guys yank the six to put in a 360. I have converted several slanty k members to the 73-76 V8 style. If you have the time, you could fix the existing K while it is in the car. You will need to measure another K member to make sure that you get the pivot shaft holes in exactly the right position. Every 67-76 K member had these holes in the same position, so any undamaged K member will work.
Regarding the suggestion that This is becoming more common...I agree. The cars are between 37 and 43 years old, have had multiple owners and were often neglected. Add to this the fact than many of us have double the power of a stock engine, stiffer suspension, bigger sway bars and larger tires. The engineers probably only intended for these to be 100,000 mile throwaway cars as well.
