98 v70: knocking cat, running rich, half detected misfire, iac, smelly fumes

[CIK7]

I thought my exhaust was loose because it was rattling somewhere at or before cat. I had a misfire on cyl2 and cyl4 on last code scan from CEL. Today SERVICE (not CEL) was on and I ran the scan. p0172, po455, p0505 popped up. No misfires today. Then got under car, shook exhaust. Something inside the cat (the honeycomb stuff?) was rattling a lot, lots of noise. Is this a bad cat? Are all those codes caused by a bad cat? I parked my Honda because it too needs all 3 cats replaced. Im gonna search eBay for a Superior(R) Volvo replacement cat. Superior has a complete kit for my Honda for $289. Looks like the volvo cat was welded on and an upstream universal would be $140ish.

Edit: it appears there is not a downstream cat.

Edit: I forgot to mention that the exhaust fumes seem to always come from the front of the exhaust and they are super smelly.