There's a guy, or at least there was, on ebay who sells the whole kits including wiring, grill, lights, switch, etc.
Some cutting is required but it is in a place no one will ever see.
Do a search. This has been covered in great detail.
it IS wider. the ears that come up between the lights and the grill are thinner on the GTs. The grill will fit, it'll just take a little persuading. But isn't that what hot rodding is all about ? I am going to keep my pony grill, but adapt it for the bigger GT lights. I love the corral, but hate the wimpy little fog lights.