BB gearbox for arm/claw

[Ned Shelton]

Our team plans on using the RS-775 to power our (simple) arm, and possibly a 395 for the manipulator on the end of the arm. We would use a 64:1 gear box and a belt ratio on the joint of the arm, and a 326:1 or 682:1 gearbox for the "hand". So my question is, will these gearboxes be driven backwards by the weight of the arm? (~7lbs at 50in) We can't find a good worm drive to use on the motors, so I was hoping the high ratio planetary BB gearboxes wouldn't move backwards, but I have no experience with the hardware.
Oh also, how reasonable is Bane Bot's 35 ft-lb torque limit for the 64:1 or 326:1 gearbox? Will I just instantly strip the gears with what I'm doing? Sorry, I know that was a wall of questions, but I'm our team's mechanical captain and have almost no experience with these gearboxes.