years ago when my mum had a AE82 twincam, I was looking for the 02 sensor and I couldn't find it. I think the aussie bigport 4AG's didn't have em... And there definitely is a difference in the tuning..my stock 4AG(jap import) was noticably quicker(in a AE86) than the AE82, and their about the same weight. my import engine seemed to have more torque down low.
if your comparing jap import fwd to rwd I wouldn't expect there to be any difference tho..