I currently shoot a very accurate custom model 70 .308 with a Hart barrel and a Mcmillian marksman stock but I would like a detachable magazine and an A3 or A5 stock. Is there a aftermarket DM system for my gun? The screw spacing mesures aprox 7.625" . I noticed FN A1 SPR rifles have detachable magazines on a model 70 style action. Would that stock and mag system fit my rifle? Do they sell them seperatly? Thanks for any help.