The 2-1 Section is longer due to the EPS system, good to hear you got it fired into life!!
Is it throwing any codes other than the o2 sensor (I'm wondering if the OBD2 Port still works with the ECU??)
Just so you know, you wont need the o2 sensor behind the cat anymore.... Euro R's only have 1 in the 2-1 section of the headers.