If the header has sagged over the years there is a problem with the method used to support it. It is normal to lay the brick down as you have described and it should be placed on a heavy enough apiece of angle iron to support it. If the span is great the angle should also have been bolted to the wall in several places to help keep it from sagging. You should remove the bricks and see what is there and either replace the angle with a larger one or add some bolts. Then replace the bricks. If you would like more details on how to do-it-yourself contact me through the "Expert Advice" section of this website under the construction heading.

Glenn Good