Hey Andrew, welcome to the forums!
If it only has RS, then it's likely just the 2WD version. One way to know for sure is to have a look at the chassis code - an "N" in the chassis code will tell you if it had AWD or not. All GT-Rs had an "N" (BNR32, BCNR33, BNR34, etc.), so the Stagea code should be WGC34 for the RWD instead of WGNC34. None of the RWDs came as manuals, either. AFAIK.
Dayz parts are mainly just options as you've stated, but I think a Dayz edition had a package of Dayz parts optioned on to it. You might be lucky and find a few little features that are pretty rare, like the tailgate interior lamp, etc.