18", six shot.
Get Vang Comp's velcro sidesaddles. They don't interfere with the operation of the gun.
Ghost ring if you plan on using it outdoors. If it's a buckshot/indoors gun only, bead is fine, though upgrading to an XS tritium Big Dot is even better.
"And Shepherds we shall be. For thee, my Lord for thee. Power hath descended forth from thy hand, that our feet may swiftly carry out thy command. So we shall flow a river forth to thee and teeming with souls shall it ever be. In nomine Patris, et fili, et Spiritus Sancti. Amen."