I don't know if anyone has kept up with this evolving project, but this guy in California has patented and is refining a 10rd mosin mag that requires no permanent modifications to a Mosin Nagant, when ever he finally finishes it, I plan to buy one and maybe work on a HB mosin project just to make 7.62x54r.net mad.
http://www.datamancer.net/mosinmags/
http://www.datamancer.net/mosinmags/