RE: Pitts 1/3 hard to turn right
If you're running the OS 1.60, I'd go with an 18x6 prop. I've got two of these engines and that's one of my main props, and pretty much the prop of choice for most owners of the 1.60. But, as was said, it's going to make MINIMAL difference in the turning problem you're experiencing. Using a tiny bit of rudder input will fix it for sure.