But why someone would like to put euro E46 M3 cats when he already have
SMALLER US cats on his Z4M from factory?
You can just put euro/CSL/aftermarket headers and get 2x o2 sensors and 1x EGT bungs weld in his OEM section 1.
The bungs can also be weld into the headers and get a tune!
It will cost less to get the bungs weld than having to buy another similar section 1 that only difference is having bungs from factory...