It should say it's a GTI on the V5, I'd trust that first as someone may have just debadged it. My old cab didn't have GTI badge on the front. I think they normally had alloys, but someone may have taken them off. Remember, the cab is 20 years old so a lot may have happened to it in that time.
If you do get it, then use the steels for winter and get some nice shiney new wheels to run in the summer, job done.
It may be just a carbed cabby i.e. clipper rather than a GTI, it could also be on the V5 as a GLI.