Listen and heed my words, so that you can learn from my mistakes and not make the same in your own lives:
When you decide to have one of your firearms modified in a manner which requires gunsmithing -- such as having the receiver of your shotgun drilled & tapped for installation of a Weaver rail -- do not assume that the gunsmith has such a rail on hand. Further, do not assume that the gunsmith can just look up the distances between the screw holes in the rails and do the drill & tap so that you can buy the rail system later.
If you make these assumptions, what will happen is that the gunsmith will decide to order the rail system, which will take weeks to arrive, and you will be charged for both the labor and the part (bought at retail price.) What you must instead do is buy everything beforehand, so that you get them at your convenience and at the best price possible, and then when you go to the gun shop you should say "Put this rail on that gun" and all you have to pay for is the labor.
I learned this the hard way, as a weekend $60 drill-and-tap turned into a two-week $115 "we've got to order the part, we'll call you when it arrives" debacle.
Sometimes I think I'd be better off if I just became a gunsmith myself so I could cut out all the crap. Sadly, I can't afford either the training or the tools.
(This isn't a Monday but I'm classifying it as a Monday Gunday post because it has to do with firearms.)