James, I am not familiar with those drivers. You might inquire at the sites that specialize in audio archeology, like AudioHeritage.com and others. They most likely know who made for Yamaha that driver. However, there are a few thighs that I would like to mention in context of the Azurahorn result you posted above.
The measurements above were made with a microphone positioned at mouth – from my point of view it is not admissible and it says about nothing. BTW, the +5dB blip at 10.5kHz is too brutal but most likely will not be there at 8-12 feet and the slightly off axis shooting. Also, and it is probably the most important – do not look for MF driver based upon it’s response. Look for the right sound “full range” (I use the TTH characteristic) and upon you found what you need then learn bout the driver response and deal with the response idiosyncrasies. Rgs, Romy the caT
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche