Hi Wolfmans,
Well, you got it out, and that's all that's important! I tried the wiggling and prying, but didn't want to risk damaging the throat plates. It helps once you can see how the clip and plates together when you have the clip off. Perhaps I'll try this method again the next time I inspect the cat.
When I had the damper open, there was just enough room for me to slide my un-gloved finger through and around the back where the retaining nut was, and just enough room to slide down the needle nose vice grips to capture it.
Your cat looks about the same condition as mine, except your steel casing isn't as deformed as mine is. Since I could get it to sit in the refractory chamber and completely close the the refractory chamber door, I put it back in to give it a spin. The sweeps were in last week, and they inspected the flue. They said that there wasn't enough buildup to warrant a cleaning, and that they'd be back in the spring, so, the cat must have been working.
Once the stove is cruising with a good bed of coals, when I stop the air down to near fully closed and engage the cat, I get about 160F coming out of the top vent ( measured with a meat thermometer, about 3" away from the exhaust port ). This is with the firebox about half full with fuel. I'd be interested to hear what you get under similar operating conditions.
Jonathan