Im looking at a 20 gauge Diana grade made in 1974 that has a round knob. All the information I have and pictures of that era show a flat knob. Was the round knob available in that era? Also: Were the B-25's available as early as 1972? I thought they didn't come along until much later. I would really like to add a 20 gauge Diana grade with a RNLT made in the early 60's before the salt guns to my collection. Are these the best era superposed to buy and is the 26 1/2 or the 28 inch the most desirable?