Hi, Gunplummer,
I sure agree about "weird stamps" but I had never heard or read about a "first quality" mark, and have a hard time reconciling it with a mass production operation in wartime. Would that rifle have been issued to some special unit, or reserved for rifle marksmanship competition or for a presentation piece?
I don't think there is much doubt about the ground crests. The "mum" is not the symbol of Japan, like the U.S. eagle. It was and is the personal symbol of the emperor. As part of his desire to keep the emperor as a figurehead to pacify the Japanese, MacArthur allowed the Japanese workers in the arms depots to remove the emperor's symbol from material that was to be turned over to the Allies, thus avoiding the disgrace and loss of face which would have resulted from its being in foreign hands.
Of course, when GI's realized that a ground "mum" indicated a rifle from a depot, disproving their stories about capturing the rifle in hand-to-hand combat with a Japanese general, they concocted all kinds of stories to explain it.
The most fanciful was told to me by a vet. He had captured his rifle in vicious fighting in the jungle (of a recruiting station in Pennsylvania). No sooner had he come home than the FBI came to his door and took the rifle; when they brought it back, the crest had been ground. It seems that Harry Truman personally kept track of every Japanese rifle brought back and wanted to make sure the "mum" was ground off, so he had the FBI round them all up and grind the crests. And, just think; he had time to be president, too. I really think the guy expected me to believe that nonsense, but I just smiled and left.
Jim