It's possible; I would have erased the codes after replacing the O2 sensor and if the P0430 code showed up, it's likely that the converter is faulty. If the converter is bad, the only "correct" fix would be to replace it. Rockauto.com is a good place to check for replacement converters; I've found some great prices there! One "trick" that some have employed is installing a spark plug anti-fouler on the end of the rear oxygen sensors. This pulls the element of the rear sensor partially out of the exhaust stream, thus affecting it's readings. It's not a guarantee to keep the P0430 code from returning, but seems to work for some and it's a very low cost gamble. Others replace the precats and exhaust manifolds with headers, which does eliminate the chance of catalyst debris being sucked into the engine, but doesn't help the check engine light issue. As far as the chain tensioner issue, if the upper chain is making noise, then "yes," you'll likely need the updated tensioner feet.