Mike, you're correct that the sliding top lock goes way back to a French patent, but I don't have any documntation.
I converted to straight grip, stocked and metal finished a couple of Savage/Valmet 20's in the 1980's and they both came out very nicely. One is still the favorite shooter of a client I did multiple projects for.
I still have a nice piece of Turkish walnut machined for a 20 ga buttstock in the don't know what to do with box....