The hood (that's what we call it over here
) clam shell, and trunk lid are the big winners. If the hood saves just under 40lbs, I'd put the clamshell at 10 and the trunklid at 15-20. The fenders would probably be worth another 20. The doors are a different issue. Those shouldn't be swapped unless you have a full roll cage with significant side bars. On top of that, you'd have to lose the windows.
The front and rear bumper covers in FG are actually slightly heavier then the stock plastic.