You've had no replies, so I'll mention what very little I know.
About 5 months ago, I bought a rifle that was a sporterized type 38 Arisaka (japanese) military rifle. I was told by seller it had an A&M barrel on it, a name I was not familiar with. Did the google search and discovered A&M stood for Atkinson and Marquart, two gunsmiths who partenered together in Prescott, Az building custom rifles, making their own barrels and etc. From what I gathered, they built highly regarded custom rifles until they had a falling out with each other in the early 70s. Seem to remember seeing one post by someone who commented that he thought $1200? for an A&M rifle (don't remember anything particular about rifle) was a bargain, or words to that effect.
