Pardon the thread drift, I've had my fill of curmudgeonous this week.
Nope, no engine pulling. You have to pull an alternator, and move the AC compressor to one side, and then both manifolds come right off that engine. It's a $400 manifold because it's a tubular header and cat in one piece. They built it that way because customers demand ever increasing power and fuel economy in smaller packaging so they need an exhaust system that is relevantly free flowing and compact. Because modern cats routinely last 150,000 or so miles the whole header is designed and built to last that long. It's in one piece because if it wasn't it either wouldn't fit, or the added flange or ball and socket joint would add turns (lowering the efficiency) or leak over the service life (wouldn't pass emissions).
I apologize if I sound cranky, but cars don't have points ignitions and cast iron manifolds anymore. And that's a good thing, it makes them lighter, faster, more powerful, more fuel efficient and longer lasting. And big surprise, better technology costs more. It's not some conspiracy by car company's to make you pay more for parts, or only hire lazy engineers. The only conspiracy is that of shade-tree mechanics that don't want to learn new techniques for working on cars.
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All that said, it's probably not the cat. It's actually pretty hard to kill those things, and if it were so clogged that it was killing your power that much, the manifolds would have been cherry red, and the engine would probably have overheated due to exhaust heat staying in the heads. Pull the plugs and post pictures to see if it's running rich or lean.