As I said before, you won't be running this prop at full throttle. Don't run it at full throttle on the ground. Adjust the engine with a 12x6 or 11x7, and then switch to the 12.75x3.75. If your airplane is very light, you can then fly this prop at partial throttle for good hovering. If your airplane is too heavy, don't use this prop as you will have to run at too high a throttle setting for hover. Max weight has to be under 3 pounds. Thanks for your comment on the 63. It's likely the most reliable in the YS line, I only wish I could get them to make more of them. They are always in short supply.
Good Flying,
Dave