I appreciate the advice John and have a question about your post after this... Yes true, well even though this guy is white South African, he still has the Aussie trademark attitude of that as I described. I don't think there would be many places in Aust that would run in and get a torque wrench. look up the correct value for that rear member and check it while you wait, it just wouldn't happen. That's why having 60s-70s American cars can be frustrating - things like this always pop up where you wish for more people who know them. Can you believe I went to a differential shop in my city (biggest city on the west coast of Australia), they had been in the same location for at least 35 years, and ALL they did was differentials. This was about 7 years ago. I took my Challenger there with a noise in the driveline. The old guy in there had never heard of the Chrysler 8 3/4 rear end !! I couldn't believe what I was hearing. So of course I didn't get any work done there.
Now, you said that, "you have to do a proper break in of the differential as new bearings build a lot of heat initially and you can ruin your new bearings and gear in minutes"
Do you mean a break-in on the bench or in the vehicle? I can't see how it could be done on the bench, even if I had a rattle gun (pneumatic socket drive) which I don't and no load on it anyway. Also, as Jadaharabi mentioned about checking the pinion turning torque without the seal, is that 20-25 in-lb you mentioned the value I should see before tightening the main chunk and before the seal or is that when the whole thing is ready to be installed in the car?
Now I can't wait to get the socket to see what the turning torque is. However, don't forget, as I mentioned previously, I still have to put in the clutch type SG I bought new from Dr Diff. This 741 was rebuilt as an open centre 7-8 years ago; now I have pulled it off the shelf and putting in the SG. So the tightness could possibly change after that, even if I didn't touch the pinion, although I can't see how (with my limited knowledge).
