Well, put 5th gear together last night. After more than one email with the Loctite tech line, settled on 648 for the gear and 277 for the nut. Initially torqued it to 250 lb-ft (that's all the torque wrench I have) as the factory specification is 250-300 ft-lbs. I then used a breaker bar and a cheater and torqued the living bejesus out of the nut. So I have a new gear, new nut with the two set screws, and the pronged retainer. We'll see how this works out.