The easiest way I've done it is to hinge them from the front using brass wire and tubing (See photos);
1) Cut a piece of 1/16" diameter brass or aluminum tubing about 1/2" long;
2) Insert a piece of brass wire about 3" long into the tubing with equal lengths of wire sticking out of both sides of the tubing;
3) Bend the wire where it comes out of the tubing on each side up 90 degrees, forming a "U" shape;
4) About 1" from each of the the first bends in the wire, bend both sides again by 90 degrees into each other, forming a rectangular shape;
5) Cut another piece of 1/16 tubing about 1/2" long and insert the two ends of the wire into the tubing;
With this method, you're going to superglue one of the pieces of tubing to the top of the radiator support and the other piece of tubing to the inside of the hood. Since all models are a bit different, you might need to put a slight bend in both sides of the wire, typically somewhere in the middle, for the wire to clear the radiator support and not make the hood sit too high in the front. You'll know if and how much you need to bend it when you put it where it will eventually be glued, working from the bottom side of the model.
6) Once the wire is bent to fit, superglue one end to the top of the radiator support;
7) Tape the hood in place;
8) From the bottom-side of the model, superglue the other end to the inside of the hood.
When done properly, the hood will open and close perfectly every time.
You may need to make the wire and tubing lengths longer/shorter, depending on the model you're building and how far you want the hood to hang down in the front when it's open.