There is a loose association between KV numbers and prop size. This is an over simplification but basically the larger the prop, the lower the KV. Mainly this is because lower KV is generally associated with higher torque, so a lower KV motor is stronger than a higher KV motor and can handle the larger prop better.
You generally cannot put an 8" prop on the motor you have because while it would likely work for a short time (minutes, I suppose), it would likely fail spectacularly in that your motor would overheat and possibly start on fire. That motor at that KV level is made for 5 or 6" props.
There's more to this, of course. The pitch has an effect, the number of blades have an effect, but in general, you have the wrong motor for the Cub or Scout.
If you want to build the MINI scout, that motor would work.