won't idle

I have a 1984 big blazer with a 305 automatic 4 wheel drive. It was running ok and then started running sluggish. Parked it for a couple of days (didn't need to drive it) and now it won't idle worth a darn. It started spitting out rusty chuncks out of the exhaust. This is the original exhaust system. It has 303,000 miles on the exhaust system. Could the sluggish running be a stopped up catalytic converter? What are the symptoms of a clogged catalytic converter. If this is the problem how do you remedy? Put new one on or take off, knock out "guts" to CC and put back on? Nothing wrong with the carb or timing or plugs.
Any help is appreciated. Thanks, Rodney

Does it have a CAT? I honestly don't know... If so, then yeah, I'd have that checked out. I would put another one on. It's the only responsible way to go. Catalytic converters don't really hinder the performance of the engine all that much.