I bought a 2003 WJ with a blown 4.7 V8 engine, and I am going to replace the engine with one that I have from a wrecked WJ. It would be relatively easy to replace the exhaust Y-pipe with the catalytic converters in it when the engine is out. However, it costs $350. Never having seen the car run, I don't know if the check engine light is on, or if there is a bad smell, or any of the other signs of catalytic converters that need replacement. How long should these last? Any opinions on whether I should change them? I would rather not spend the money right now.