It's not a stoeger, but here's my stevens 311 that I hacked up the same way you're thinking of doing:
IIRC, the barrels are just under 20" and the OAL is almost 30" because I didn't want to go too short in case I ever tried to redo the grip so it's not so ugly looking and had to cut some more off it.
Obviously I did a really, really lousy job. I didn't even cut the barrels even. The gap between the barrels was filled in with some type of metal epoxy stuff, and still looks bad. The grip came out bad because I didn't take into account how the stock was held on when I started butchering my poor gun, and had to cut the bolt down and have it rewelded before I finished putting it back together, so it's not very comfortable either. The wood and steel were spray painted. I'm still trying to find a sterling silver or pewter skull from a necklace or something to attach as a front sight too, to complete the tactical hillbilly look.
As far as shooting it, it's pretty lame. I used to have a moss.500 PGO that busted my lip. After selling that one, I kept reading that the PG style shotguns kick more than the grip style that's on my SXS, so after getting this 311 in fairly rough shape at a decent price, I figured it'd be a good project since I always liked the looks of these kinda sawed off shotguns. Now I have a gun that's as ugly as it is useless....but I still think it's awesome
.
Not sure how heavy the receiver is on the stoeger, but the stevens is WAY heavy and much more difficult to open without the extra weight of the longer barrels now. I haven't shot any standard power buck or slugs through it yet (mine is only a 2 3/4" chamber too BTW), but this one does seem to kick considerably less than the PGO 500 I had. That may be because of how heavy the receiver on the stevens is though.
I planned on carrying this thing in a scabbard (most likely a modified arrow quiver) on hikes, but because of the weight and uselessness of it, it mainly just sits in the safe and collects dust. I wish I had hacked up an NEF single shot instead, although that would be considerably less cool looking.
Depending on what you intend to use it for, you should think long and hard before you cut the stock down on your gun.