Re: Looking for help 12' v Mirrorcraft "Unstable"
I had what looks like the same boat as you, about a 1965 or so Mirrocraft 12 footer a while back, it would rock a bit but never flipped, it was far more stable than many other 12' boats I've had. My current boat is decent but not as stable as the Mirrocraft was. However, I would never even think about adding pedestal seats to any 12' V hull. I even took out the clamp on seats I had to put my weight lower in the boat. I'm also not a big fan of adding weight to a boat, the right answer is to redistribute the weight you already have.
I built removable floor sections for mine at first, but ended up removing those and just tossing in a few pieces of foam runner to dampen noise a bit. In my experience, adding weight to an already unstable boat usually makes it more unstable, maybe even unsafe.