According to the website I'm looking at, GTA wheel backspacing is 4.75" front and 5.25" rear. If I were you, I'd buy either a 1" adapter, bringing the rear wheel BS down to 4.25", or even a 1.5" adapter. 3.75" backspacing, 4.25" "Front"spacing, from the outside of the car it'd look like the rear wheels stick out as far as if they were 8.5" wide. I think if you spaced them like that, you'd have the usual GNX wheels but you'd have a pretty unique staggered look. Hell, you COULD even run 2" spacers, fill up the wheel well as if the wheels were 9.5" wide. All depends on how you want it to look, the adapters give you all those options.
I dunno if you're familiar with all the wheel measurements etc, if the numbers are getting a little confusing, I'll help you pick the right adapters from the vendor I used. They're $80 for a pair, much better than hunting down another set of front GTAs in my opinion.
Here's how my wheels look with the adapters. These wheels were NEVER meant to fit a GN.