I think the shaft is 1mm. The outside diameter of the bearing must be 3mm. I was afraid to do the bearing mod if it makes the gearbox weaker. I already broke my gearbox twice, I don't need to make it weaker.
Now, about your other question about the prop. I broke my vapor prop and tried everything I had. The cessna prop works very poorly. It has less thrust and it will not spin as fast as it does on the cessna because of the different gearbox. Besides that, you don't want the vapor to fly faster. It flexes the main wing or something and heads for the ground. Then you pull up and it goes up too much. High speed makes the vapor hard to fly level. It flys best slow. I would like to try the vapor prop on my cessna and ember but the gearbox has different ratios and I bet the bigger prop will overload the motor. It will be trying to spin the big prop too fast and won't be able to do it causing it to draw too much current. I am going to put the vapor gearbox and prop on my ember if my order ever gets here. The slow guy that is delivering your vapor must have my stuff too.