Exhaust and O2 woes

[poorboy08]

First time poster and first time reader, so please forgive me if this is in the wrong section.

I have a 03 GT and just recently while driveing had a piece of metal get underneath my car which severed the wires to the rear O2 sensor as well as put a hole in my muffler. I'm going to replace the muffler with a stock piece, that isn't a problem, what I'm not so sure about is the rear O2 sensor. I briefly looked under neither the car and noticed there is a rubber boot that goes up into the metal on the underneath of the car. The 4 wires that were cut are all exposed but I was not able to see where and or how the rest of the cabling is routed. What all is involved with changing out this O2? I have a Bosch replacement, but they (auto parts store) says it is not an OEM replacement part. Is this going to be a problem or do I just have to do some fancy wiring? TIA!