Yes that is correct the low speed needle is the short one and the high speed needle is the long one.

I have taken two different fuel jugs and mixed them together before. You could take the Byrons fuel and mix it with the FAI fuel to get something like 7.5% nitro fuel with a mixed higher percentage of castor oil in it.
But yeah the K&B engines may like more nitro in them, I forget at the moment. I have a old K&B 65 I got years ago. I bench ran it for a while using 5% nitro fuel and it was running OK. But I never used the engine after that though.

Anyway, it doesn't really hurt to run the K&B engines with FAI type fuel and see what happens.