That 2 speed won't stand 10 seconds under a 1717 , so ditch second gear. Lock it in first and ditch reverse also. I doubt the motor and esc would work well as brakes on a truck that size so i hope you plan on mechanical braking right? For mounting the motor your best bet is probably to make a custom motor mount out of some angle or see if mike can whip you up something. I've never really seen a GST 7.7 up close so I'm just kinda spit balling here.I'm sure someone else can give you a more detailed answer.--Josh