A few of us on SKS Boards have been working out Duck-bill-less technology on the conventional SKS, primarily using modified Tapco Mags, and have come up with some excellent working models. Just thought I'd share the news.
http://www.sksboards.com/smf/index.php?topic=68912.0
http://www.sksboards.com/smf/index.php?topic=68912.0