I have a friend whose 2011 Honda Odyssey with 68,000 miles is repeatedly throwing P0420 and P0430. She had it diagnosed as needing the catalytic converters replaced. I pulled the codes, and it does seem like the downstream O2 sensors are moving too much. She doesn't have the cash to have a shop do it, and the cats are like $200 each. They are basically attached to the manifolds, one between the engine and radiator, one between the engine and firewall. How hard is this job? Is this something that I, as reasonably competent guy can handle? I have been servicing my own cars my whole life, but I would like to have a little more insight before I try to attack a potentially huge project on somebody else's car.