I'm going to assume that your receiver isn't tapped for a scope rail.
Just fwiw, you can buy a moss/mav scope mount with screws on ebay for under $7 shipped. And an 8-40 tap and #28 drill bit for under $12. I am currently waiting on the parts to do this to a different shotgun that I have (not a Mossberg, but also not that it matters).
It's as simple and marking where to drill the holes, drilling 4 holes, and then screwing the tap into the holes by hand. And if you don't have a tap, use the screws that come with the rail and achieve the same thing. Either way, you're just threading some holes in aluminum.
Seriously, it is less than a 10 minute task. Just make sure the bolts don't protrude down into the receiver where it will affect the barrel being inserted or removed and won't interfere with the top of the bolt. If they are, file the bolts down shorter. When you're finished, remove the screws one at a time and Loctite them and you're golden.