WTB New/Used Cat

[e3091318is]

Long story short, I have had a 1222 code I am in the process of fixing and need a cat to throw on the car to pass smog.  Had a cat put on before and the muffler shop said it was the car, but I have doubts.  Would a rebuilt engine be running rich to a point to cause the cat to burn up within 1000 miles?  The exhaust also sounded a little funny when I picked up the car but I thought it was my muffler.