look at the VIN plate on the firewall... if it starts with BNR32 its a GTR... as for if its a V-spec that would also be something you can find out from the VIN plate...

ALL GTR's are AWD, unless they have been switched to RWD only...

and dropping in a RB26DETT is no simple task... there is ALOT of wiring that is involved

 

If it is AWD then most likely it is a GTR as most would not go to the trouble of changing the entire driveline into a gtst or similar. Also as said the build plate numbers will tell the story if you know how to read them. I think also the hydraulic Hicas rear steering was only on GTr r32 not other r32 models.

 

Hicas was on almost all skylines after 1986

also there was a AWD GTS-T called the GTS-4 which has an RB20 engine it also uses the same ATTESSA-ETS controller as the GTR

if by chance he has swaped an RB26 into a GTS a couple other things to note are the rear quarte panels... on a GTR they are wider... and the hood on a GTR has a very small cowl and will not meet up with the front bumper... but that is easily changed with swapping the hood...

the easiest way is simply looking at the VIN plate, it should be Blue and on the drivers side of the firewall

 

Another way is to see if there is an instruction manual for the car, that should tell part of the story. Also, you could try looking at the VIN like the other guys said or checking to see if the car has an ATTESA ET-S system installed. If the car don't have Attesa-ETS then that's something to be worried about.

You should just simply, however, take the car to a mechanic and get it checked.

 

Look at the Transmission; if there is not transfer case with a front driveshaft and front differential,in the oil pan, then it is not a GT-R. A GT-ST4 had an RB25 not an RB26 in the AWD platform . If a swap was made, then check to see if the original VIN is a form of BNR32-xxxxxx,[the "BN" is the key] if not then it is not a GT-R.

 

wrong it was a rb20