I just got done removing the baffles on my 550 yesterday, and it was a bittch!!
I drilled out the 3 screws and it was just a cover plate with a another plate behind it. I ended up drilling about a hundred little holes around the edge and pounding it out. Then I had to weld a slide hammer onto the center pipe and ripping the center of the baffle out. It wasn't fun. I can send a picture of what the core of the baffle looked like in a bit.