P0420 and P0302 and Timing Belt Problems

Hi,

I recently got a P0420 code from my 97 Camry LE (has about 130k on the clock). I had replaced the cat about 2 years ago, and since then I have put less then 1000 miles on it. My car is a CA emissions one but I'm driving it in NJ so I figured I wouldn't need the extra expense of the CA cat and it needed to pass emissions so I relaced the cat with a non-CA one...

I think the timing belt is on its last legs as for about 6 months now I can hear it slapping around, but I figured as the engine is non-interference, then when it breaks it shouldnt do too much damage.

I took the car out yesterday for the first time since the P0420 (cat efficiency) code triggered, and on the way back from the store, the Engine light began flashing. I had my OBD in the car & hooked it up and it had given me 2 misfire readings & was running rough. By the time I made it home (5 miles away), the car was shuddering at traffic lights on the point of stalling. It also lost a lot of power when driving.

Could a 2-year old cat be the cause of the problem or is it likely to be the timing belt and/or plugs wires?

Any help would be greatly appreciated!

Thanks!!!