RX8Club.com - 98 Mustang O2 sensors

I know this is a bit of a long shot, but can anyone tell me how many O2 sensors are on a 98 3.8L mustang? And more specifically where are they?

Basically my BF and his uncle insist there are two. The Haynes manual seems to indicate there are four but for some reason is incredibly unhelpful in pointing out their locations. And I had a '98 Taurus that was given to my little brother in 2008 and I remember a few years back hearing my grandfather b****ing up a storm about replacing the O2 sensors on it because two were easy and the other two were near impossible.

The mustang is getting CEL P1151 and he changed two of the O2 sensors, the air filter, some vacuum hoses, and cleaned the MAF sensor but is still giving that code.

Helpful tips are appreciated, he's trying to fix it up so it can be inspected and sold to a different uncle before the end of October. Thanks!!