It should be fine. The grappy speed 300 (6V version) is an excellent motor.
Just install it and run it without any load and keep your finger on the fets/heatsink. If it gets hot quickly, then remove the motor. If it doesn’t then give it a go installed but still free standing. If it’s still ok, then do a few runs without any hard breaking/stopping/starting. If it survives that then you should be fine.
A couple things to do to the grappy to make it even better. (learnt from my RC18T days….).
Oil the bushings on each side.
Break the motor in for 30 – 60 minutes using 2-3 AA’s.
Good luck dude!
ph2t.