This system is actually called Rock M-14 SOPMOD, designed by Mike Rock of Rock Creek Barrels. Mike made it at the request of Crane NSWC, but Crane noticed Mike was using a Sage buttstock assembly in the conversion and decided to cut some of the fat from the bid by going directly to Sage Intl and having them make a similar system. They went with Sage's design. Sage was also better equipped to put this out in the needed quantities.
Regarding the gas system, it's just a standard M-14 gas cylinder that has been moved rearward and canted. The idea is that this redesign eliminates the double bend in the M-14 oprod (oprods usually break or crack at the bend due to the torque). An M-14 oprod is shortened by cutting the bends out, so the gas piston now impacts the oprod where the first bend off the receiver would normally be. The result a straight oprod, and the gas piston and the oprod are in a direct line. Less torque and the oprods won't crack at that bend. There's no modification to the receiver, just the barrel and a few parts. The conversion can be reversed with a new barrel, oprod, oprod guide and spring (and a standard M-14 stock).