I'd do all you said, and then get it idling properly with regular gas, then a highway run and straight on to the rollers.

Exhaust leaks around the O2 sensor could make you rich, but I don't think it would be this bad.

Gaskets are MD181032, MD124675 & MB687002 - did you try Ziggy?

Crappy tire sells Pemratex UltraCopper.
I wouldn't bother using just RTV. You'd have to get rid of the old gaskets and everyting will be apart so you might as well do it right with gaskets.