I have seen two shotguns set up with a telescopic sight both the standard 12 bore. Each gun had a companion though the chances of them staying together would be very much against because of our licencing laws. Each of the guns had a full length rifle sleeve for one of the barrels each gun it was the left. Going by what I was told this setup was useful in the field for the odd deer. One of the guns I became familiar with for a time was a Webley & Scot box lock that I fitted a replacement stock, its original stock had a planted on leather cheek piece not of the best workmanship. Sadly I was there when the rifle sleeve was cut up for scrap, to own such a gun having a rifle sleeve you would need to have a firearms licence as well as a shotgun licence so making the guns prospect of a sale very small so the sleeve had to go.
I still have the stock that was removed from the gun so I will post a picture in a couple of days of workshop storage box hunting.