Hello, Dave.id,
another leftie (who started up shamisen recently) here . There is a great article about lefthanders playing shamisen in the Bachido blog section, with some tips: https://community.bachido.com/t/can-left-handers-play-shamisen/2546/1
It helped me a lot, when deciding, whether to start with shamisen, or not. There are also comments from other lefties. It might be helpful for you too, try to check it 