Just another small 'push' trying to find the OP find an answer.
Learning fingering should be no big deal.
I don't think MIII music is usually written with a particular fingering in mind.
So: another small 'plug' for the Abbott teaching material.
It's possible Abbott's books could have been written with the reversed layout in mind??
I reckon a man with 27 Concertos (i?) for accordion behind him has to be worth a try.
By the way:
It's arguable that a layout putting the higher notes under the more agile fingers is a bonus.
You could see your mistake as a huge piece of luck!
Richard, thank you very much for your information. I tried the sample page and it works for my reversed c griff bass.
By the way, would you have more information of the man with 27 concertos? Thanks.