The 83 Japanese engine is more of an American/Canadian version than the ROW cars. Hence, the lower hp.
I don't know all the details and I may be talking out of school but I believe the ROW cars have a little more compression. Later US SC's have 9.3:1 compression and I believe the later ROW cars have 9.7. They breathe better and more fuel is distributed. There is more total ignition advance. (I qualify all of this as suspect as I don't know for certain). Pretty sure your car will have the Lambda system (O2 sensor system)
There are threads in here where guys know the exact differences. Most comparisons will be ROW vs US but that will get you a pretty good picture.
In the way bottom of the PET parts diagram there are tables of what is what as to engines on a macro scale. Here is a screen shot of the 83 engines.
