I don't think a Grand Prix is remotely worth the effort and money, but it'll work, after a fashion. There are zillions of much better old steel bikes/frames you could pick up for a song. The Grand Prix wasn't even a good bike in its day. Now, they're basically junk. Like I said, it'll work. And you'll learn a lot. You'll have to, cause there will be lots of fiddling with it.
Edit: to be clear. I speak from the pain of my own experience. I don't mean to dissuade you from this sort of project in general. But I can't endorse fixing up a Grand Prix in this way. It's not worth it.
Last edited by grolby; 03-13-16 at 08:50 PM.