Well, that was a fun learning experience. I believe I drilled out about 150 rivets in order to extract the wrong nut plates. (In case you weren't reading prior posts, I assumed that a K1000-3 was smaller than a K1000-06. Silly me.)
Per advice from VAF, I punched out the remnant mandrel from the LP4-3s. I used 1 penny nails and a cleco plier to push the 'pit' out for most of them as I was afraid to swing a hammer in the general direction of my work pieces. There were several that did require a long punch (actually the mandrels from previous rivets) and a steady hand and good faith that I wasn't going to bash my stabilizer, but good results were to be found. After that, a #30 drill wielded with a precession motion was most effective in twisting off the top of the rivet. A pair of old diagonal cutters to pull off the tail did a nice job. The flat rivets required drilling out and I didn't do too badly with those either. I used a #52 to make a pilot hole, then popped the head with a #40, again using a precession motion of the entire drill.
The most satisfying part of the whole thing was putting the errant nut plates into their correctly labeled bin for later use.
Re-assembly went well, as it would be expected, since I had the practice. Hinge hardware was bolted and tie-wrapped into place as specified. I also removed the nose piece and tweaked some of its edges so they would sit tighter against the main skin.