I recommend going to a cookery site and looking it up. The above instructions do not sound like enough cooking at a high enough temp for such a large turkey.

My method was to stuff the turkey front and back, truss it up and put it in a bag. In the old days the 'bag' was by making parchment paper out of supermarket brown bags, but now that brown bags are hard to find and the making of parchment paper takes time and lots of butter, I would go to the roasting bags you can buy in the supermarket. They are made out of some magic hi-temp plastic. I've used 'em with no problem.

It is simple, results in a self-browning thoroughly cooked and juicy stuffed turkey, but it does not in my experience result in much spare fluid for lots of gravy. What I did was to chop up and boil the giblets with veggies such as celery and onions, strain 'em and make gravy from the stock. You then season to taste and thicken with either flour or cornstarch.

Again, you should look it up, but my memory calls for an oven temperature of 350 deg F and a cooking time of 15 minutes to the pound for a turkey in the 20 lb size.

These days the television cooks have a separate meat thermometer and they test the bird for doneness according to its internal temperature. Again, look it up.