o2 sensor question

I'm looking to find a stock header, and stock cat, and I wasn't sure if an o2 sensor went into the header and 1 into the cat, or is it 2 in the cat, and none in the header? I have a 2000 GSR. A couple people offered me a cat and a header, but there was no bung for the header, but there was 2 bungs in the cat. Thanks for any info.

Todd

1 in each

In my 97 LS theres a bung at the end of the header and one at the end of the cat. It should be the same setup for the GSR.

BTW, why are u looking for a STOCK header????