The newer 870 Tacticals come with a picatinny rail nd a GRS installed, but my 8 year old 870 Express does not. I really don't need a rail, but I would like to put a grs on my 870 (the receiver is not tapped for one), and maybe change the bead sight to a better front sight. Is this possible, and is it easy to do? I don't want to drill into my shotgun unless I am confident I can get the sight on.