This is inadvisable unless you can be absolutely sure that the pencil marks will be covered up by the frame. Those who must, should first hold the picture up to the proper height, then mark lightly along the top edge of each frame. The picture may then be set aside without the need to re-measure. Given your placement decisions, hold it up by the sides of the frame in the area where you want it to hang. A friend could be especially useful now, to hold the picture while you stand back and see exactly where you want it to go.
Different people use different schemes for hanging wall art.
Some like to have the top edge of each piece exactly level with every other piece, others like to have the center of each piece exactly even with the level of their eyes when they are standing. The method described below is commonly used in art gallery exhibitions. Remember the eye wants order and this is the time to establish it. Hold up the art work so that the geometric center of the image is five feet and two inches high. This allows for most people to look directly into the picture.