It is usually not that hard to move the pattern 8" at 40 yds, but moving it 8" at 16 yds will be a challenge. Since it looks like you are stuck with the gun, I would sure give it a try. I have successfully moved the POI on several sxs guns, so I know it can be done. I had Brileys make eccentric chokes for one gun, and they definitely moved the pattern, but they moved it way too far. A guy on another forum told me how to file it to move the pattern, and I would rather do that than to buy eccentric chokes.

Filing the choke utilizes the same principle as eccentric chokes. The idea is that a change at the very end of the barrel can cause the wad to go in a slightly different direction. It's the same idea as damage to the muzzle of a rifle can change where it shoots. In a shotgun, this will only work if you use shells with a plastic wad, but most of us do that anyway.

Fwiw, here is an explanation of how to file a choke and move the POI:

Put your barrels in a vice and face the muzzle end. Your left barrel is shooting to the left, so you want to move the POI to the right. You do that by filing the inside of the barrel right at the muzzle.

Imagine the image of a clock placed over the muzzle. The left barrel is shooting to 3 o'clock now, so you want to file it at 9 o'clock. I use a round chainsaw file, and start by making 4 strokes at 9 o'clock. Hold the file at a 45 degree angle and you will be removing metal from only the inside edge of the barrel. Next, make 3 strokes at 10 o'clock and 3 at 8 o'clock. Then make 2 strokes at 11 and 7, and feather it to 12 and 6.

What you want to do is to create a chamfer that is deepest at the direction you want the pattern to go, which is 9 o'clock in this case, and then slopes to no chamfer at 12 and 6. After making the initial cuts, fire a test shot and see if the pattern moved. If it didn't move far enough, file again. Keep filing and keep shooting until it centers.

You will probably have to get the choke to a knife edge at 9 to move the pattern as much as you need, and even that may not be enough. It's good that your gun uses choke tubes. If you don't want to risk one of the tubes that came with the gun, you can buy a tube for about $20 and that will be all you are risking. This procedure will degrade the pattern to some extent. If you want modified performance, start with a full choke tube.

Good luck with it.