I've never heard of skywalker arms either. I would want to know more about the manufacturer and when it was made before buying it as well.
The open-bolt guns that were made pre '82 or thereabout, were not as easily convertible to full-auto as most would have you believe. For example, on the Demro/Wasp carbines, the fire control mechanism is sealed off and can't be modified without cutting the metal housing. On the open bolt Mac's the fire control parts can't be replaced with full-auto parts without milling/drilling the receiver.
The problem was that folks figured out how to jam up the mechanisms to make the gun fire full-auto only. My point in saying this is that IF the Sten was made around the time that the open bolt guns were being manufactured, I'd look for something done by the maker to make it difficult for someone to simply swap out a few parts to make it go full-auto. And, I'd ask over on Sturmgewehr.com (if you don't get a good answer here) about the manufacturer. Lots of those guys know "who's who" in the NFA world going back into the '70's.