Hi Mike, As I recall, Ed Tinker and George Anderson are two folks who are pretty knowledgeable about the Nambu's... Ed is in Oregon this week and is only checking in occasionally... but George is usually on every day.
I can't help you at all here, because compared to German guns, Japanese guns have always looked to me like they were made by convicts with files inside a prison in secret...

Not exactly high quality.
I have never had much of an interest in them...