Stockholm has a very capable shop. Chris can most likely help you out. I was out there last week (8/11/17) and he was building up a stock moto for a customer. Mark Enderlein at River Lake Racing may also be able to help you out.
You can run a shifter kart at Stockholm in their Outlaw class. There is also an active shifter class in the MAC acutocross series. I just built up an X30 shifter for autocrossing. I do practice days out at Stockholm.