Alright, here's a basic run-down:
Model:......................Driveline:...............Engine:..............Chassi
Code:
RS Four S..................AWD manual..........RB25DET Neo......WGNC34
RS Four V..................AWD......................RB25DET............WGNC34
RS Four.....................AWD......................RB25DET............WGNC34
RS............................RWD......................RB25DET............WGC34
25X Four...................AWD.......................RB25DE.............WGNC34
25G Four...................AWD.......................RB25DE.............WGNC34
25X..........................RWD.......................RB25DE.............WGC34
25G..........................RWD.......................RB25DE.............WGC34
20G..........................RWD.......................RB20DE.............WHC34
So, basically, when it comes to model spec, "RS" is anything turbo, "RS Four" is turbo AWD, "Four" is any AWD, and "RS Four S" is turbo AWD with manual (series 2 only, and there were NO turbo RWDs).
As far as chassis codes, series 1 all had an "E-" prefix (such as E-WHC34), and series 2 all had the "GF-" prefix (such as GF-WGNC34).
WHC = RB20DE power (the lowest model and in one spec level and RWD only)
WGC = RB25DE or RB25DET power, and RWD only
WGNC = RB25DE or RB25DET power, AWD.
So, H = RB20 power, G = RB25 power, and GN = RB25 + AWD.
All this info was found RIGHT HERE, and I will update the first post when I have time with more specific details regarding release dates, spec levels, and options.