Thought I'd post an update to my own query...I emailed Gemeinhardt and got a very prompt reply. Nice to see that customer service isn't dead everywhere.
The flutes are essentially the same. The 3O black has offset G key, B foot and silver riser and lip plate. Plus off course the black nickel plating. The 3OSB has a solid silver head joint, offset G key, B foot and silver plated body.
I now have a 3O black on order...
Re: Gemeinhart models... 11:56 on Sunday, February 24, 2019