This plane was a Type 27 captured by Finns and modified by removing the ShVAK guns and replacing them with machine guns in non standard installation. So, the waste shell slots are not standard, and the barrels protrude from the wings in non standard way.
I've just uploaded some pages on I-16 yesterday, and I'm still working on it.
I-16 family
There, you can go to the page on I-16 types here
Polikarpov's I-16 types, each type is briefly described and it has its own page linked with newly drawn views. I think that this can be of help.
A general technical description with deep details is still to do.
Regards
Massimo