I'd go with the 16x6, but for break-in you might want a 16x4 if you are bench running and not flying it in. I would recommend running 6 full tanks through the engine prior to flying it, and set the engine per the running instructions at www.ysperformance.com A little extra time running the engine on the ground will pay off in the life of the engine. They can be flown in, but I'm old school and believe in static running of any new engine.

The OS F and YS#4 are exactly the same plug. OS makes the YS #4 for them. The ONLY difference is the marking on the plug.

Glad you got the engine, now go have fun!!