Hi 450 366,
I just checked yesterday on www.egun.de and there is a gunsmith offering conversions to double rifles with adjustable barrels. I think he uses Simson shotguns on a regular basis. He charges around 2ooo,- Euros if You supply the shotgun. You can have a look at his auction when You search for Art.-ID 1097420 or if You browse from the homepage, click on button "Jagdwaffen", then on button "Büchsen", then on "Doppelbüchsen" and You will find his auction under "Doppelbüchse PGH Suhl 8x57 IRS-8x57IRS".
Hope this is interesting for You

Kalunga

"Wicked good hunting"