WOW....You have what I consider to be the most desirable rifle to be found. Others may disagree but it really looks great to me. My knowledge is limited but I believe that Bill Large was the premier barrel maker of his time. I think that it is a late barrel, maybe from the late 70's. The J.J.J.J. was a mark used on the later barrels and I think that the L was for radius groove or special rifling treatment (Bob Roller would know). The lock and trigger by Roller are simply the best made...I think, ever. These are the best parts made and appear to be well assembled. Please do not ever change the finish, (patina) as that look is really great. You have what I think is the "holy grail " of ML rifle finds. Treasure this rifle as it represents the best years of our sport.