Picked up an old C2500 with 240k, runs great. Failed smog due to way high HC (~230 when max is 96). Passed on CO and NO. Tester recommended adding a new catalytic converter. Apparently a shop will do it for ~$300 but I kinda want to do it myself. So, the question is which one do I need? A cheaper "universal" one or more expensive 50-states CARB compliant one? Already did a tune up with new plugs and cleaned TB and added some injector cleaner to gas tank.