On RPM difference between a CCW engine and a CW rotation engine - as seen from out front - may involve several things.

Shaft opening and closing time may be biased to favor the 'stock' rotation direction. Usually, for general usage engines, he difference is not very great.
Flow in the lower crankcase may also have been developed to favor 'stock' direction - things like the rod helping sweep intake flow into the 'case, then sweeping it into the bypasses,

Wear patterns may have formed if the engine was run much before reversing rotation. These will need some running to re-establish best fit. This process will wear the parts a bit more than they had worn; it's another "break-in."

"LH" props are not available in as many pitch/diameter forms, and a best-match of 'stock' engine and available props may not be likely. Even from the same maker, LH or reverse rotation props of identical pitch and diameter numbers may have different enough form (blade shape, airfoil, etc.) to cause a loss.

Then, too, unless you are seeking ultimate power, you can needle the faster of your opposed pair slightly richer to match the other, well within safe settings for dependable life for both. Check that throttle response stays consistent.