Do not, and I repeat, do not run this engine in "four cycle" mode during break in. This is what DR1 is referring to when he says you'll ruin it. I don't care what the instructions say, you should never run an ABC engine sloppy rich. The problem is that the metals in the piston and cylinder wall need to expand during engine running, causing the correct "fit" between the two. When the motor is ran too rich, too much oil enters the firing chamber, and keeps the piston/cylinder too cool for this fit to take place. Therefore, the cylinder never really expands like it should, and the piston/cylinder fit is too tight. Running the engine like this for too long puts too much pressure on the con rod assembly, and can definitely ruin the engine. That being said, run it rich up to the point of four cycling, but do not enter the four cycling phase.

As far as props. On both of my OS 40 LA's, I run 10 X 6's. When I want to go really fast, I change to a 10 X 9, and the engine handles both props extremely well. I can't go any bigger, as these engines are both on the same plane, and any larger diameter will cause the nose of my fuse to be cut off

You will not get speed performance from these motors, no matter what prop you run, unless you run two of them together , or it's on a plane under five pounds.
JMO.