Russ, If I read the details correctly (no guarantee) the new improved lock features a leaf style mainspring, rather than a coil mainspring. So, more traditional, kinda like putting an L & R RPL lock on a T/C.
Why drop the 1:66 rate of twist? Well, if I recall correctly (again no guarantee), from talking with Greg Roberts (Hawken Shop), 1:48 is a fairly traditional twist rate for Hawken rifles. Evidently massive powder charges were not so typical 150+ years ago as they are now (except possibly in Africa and India.
John (Bigsmoke)