General LSX Automobile Discussion - What part# for Denso o2's?

I'm looking to do a tune up on the Z28 I just acquired, more of a preventative maintenance kinda deal, and the o2's are one of the things I want to replace. I've read about Densos and will probably be going with a set from Amazon, as someone said they bought a set for around 38 a piece on there, however I don't know which ones to go with. Amazon says both the 234-4087 and 234-4025 sensors fit, but which ones should I get for the pre-cat sensors? Thanks.

Rockauto has them for $34.

Hmm indeed they do, and it looks like I'll need one of each part number, as long as "upstream" really means pre-cat. Thanks for the heads up.

Upstream dose indeed mean pre cat.