Stock venturi is large, about .305". Still, it can work and many fliers use it as is. Mine are downsized to around .285" either by replacing it with a Jim Lee venturi (see vendors section) or drilling out a venturi from a Brodak .25. Stock NV will work fine, a Randy Smith NV will work better. Stock spray bars sometimes have a burr on them which can prevent them from closing all the way. Check to see if your NV is closing all the way by blowing through the spray bar while closing the needle. If it doesn't stop the airflow, clean up the burr and try again, an easy fix.
Previous prop recommendation is good I prefer the Billy Clubman 10.5 x 5 prop. I would stay with your higher castor oil fuel despite the higher nitro content. As I posted earlier, Brodak 40's like more castor especially when they are not broken in. I'm out.