I was jamming with a fellow who claims his guitar was a J300 Gibson. This guitar had a double parallelogram as a inlay. It was much the same as my 1956 Country and Western Gibson neck. I did not look the guitar over in detail but the person that owned it bought it used in 1954.The guitar was an arch body style and was very good to play slap chords on, which it was supposedly designed for, thus the reason that he bought it. It had no electrics on it like the L 7 did but I do not know what year it was built. I will see him again, probably when he comes camping next year, as this year was the first time I had met him. The man that I met is almost 80 years old and I really have no reason to doubt him. He did play in his own band back in the 50's amd that is why he purchased the instrument. I will try to find out more information on this guitar if I can. This year was the first time I heard about a J300 and that is why I was checking it out on the net. I am not sure whether this helps or just confuses you more. I will try to fid out more info from him if I can.