I have received an answer to my question. The cartridge is apparently a prototype made by Miyabi for Mark Levinson. And for $1500 they will rebuild it to the specs of the Miyabi Standard ($4000 new). I'm happy.

John

Now convinced, thanks to help on another site, that the cartridge I have is #280 of the production run Miyabi did for Mark. Still a special piece, but not really a collector's item. To correct another mistake in my post, the Miyabi Standard is going for $3200 or less these days, not $4000 as I believed earlier.

I'll give it a spin on the new (to me) Sota/Rega combo and see if I can get some music out of it.

Thanks for all the valuable info.