[pmangels17]

One easy way would be to use gears like these that are designed to press onto the output shaft of the motor, and use 32DP gears to handle that first reduction. In my aspiring-to-be-a-professional opinion, I would not do what you mentioned doing for interfacing with the 775pro, or really any motor, especially if I didn't machine it myself to exactly fit. In any case, you'll probably have more luck just pressing on a gear that was designed to attach to the motor. Also, since this is a custom gearbox, make sure you cut away space in your gearbox plate to accommodate the vents on the front of the motor. What are you trying to do with the gearbox?