Some checking done
My fault on the codes,I didn't get the print out from the machine and my man can't remember,I have never had a code come up since I removed the cat,I don't believe I have any O2 sensors after where the cat as I was there when the cat was removed.
My car has 2 welded steel exhaust manifolds and there are no mounting sockets for the sensors anywhere.
Did the inline six ever have 4 sensors?my research tells me only 2?,well for my european model anyway.
With the exception of the cat removal the system is BMW end to end,thanks Ed.