another ? about my 1st 741 build

The depth should be at the indicated distance when the pinion is torqued fully and this normally means a rotating torque figure of 15-20lb feet without the seal installed. BTW, you need a rotating torque type torque wrench to measure this. Not a normal torque wrench... If your backlash is tight when the pinion isn't torqued fully you're already off. Can you post clear pics of the patterns?