02 sensors

I have a '98 Caddy Catera and I need to replace the O2 sensor(s). The dealer want's an arm and a leg (not to mention my first born child) to replace the two blown ones. I'm a pretty good DIY type of guy. Can anyone tell me the location of the coverters. From what I gathered from the dealer 2 are on each side of the manifold coming out of the engine. And the other two are on each side of the pipe after the catalytic converter. Can anyone firm this up for me regarding location.

Thanks
llglove1