First of all, are you sure a mid-rib bead is going to be really helpful?
They are generally only fitted to trap guns and, at the sporting disciplines, general opinion is that you should shoot with a natural pointing action, and that you should be concentrating on the target rather than the rib.
Secondly, fitting such a bead isn’t really a DIY job.
It involves drilling a small hole in the rib, tapping a thread in it, and screwing in the bead.
For this job you need a drilling machine with an accurate depth stop, and a means of holding the barrels in a machine vice without damaging them.