you could prolly swap everything out and make it look like a mk1 if you really wanted. The real kicker lies in the radiator support. It ties pretty much everything in the front of the car together, the lights mount on it, hood latches to it, grill bolts to it, yada yada yada. So, unless you want to do some major surgery, you can't make the lights and fenders from the old car hook up to the new car. Aside from that the basic frame is probably the same. The fender line that comes down and follows the outside edge of the headlight will not match up with the old bumpers in any way shape or form. The only way to get an RS front bumper to on your car right now is to glass your own.
Those who control the present control the past, those who control the past, control the future. - George Orwell, 1984.