Why would you need O2 sims if you have cats? I'm confused.
If you put a cat in the system you might as well just run O2 sensors and leave the cats / sensors in all the time.
'03 330i ZHP - Stock-ish
'02 330Ci - Megasquirt 3, M50 manifold, Kromer Kraft headers, Motons, widebody, etc.