The engine is still running rough and its high mileage so I'm willing to take a chance on Seafoam. Given that she ran with a serious oil leak/vacuum leak for multiple oil changes there is probably an ungodly mess of carbon buildup inside. I'll take the chance on the cat as I live in an area w/o emissions testing and I haven't seen any reports of cat damage.
The valve cover is leak free today even after another two hours of in-town driving. I still sometimes catch a whiff of burnt oil when I pull into the driveway but nowhere as bad as before. Probably just the previously leaked oil cooking off.