I have 4.10s going in next week. When I ordered the gear install combo from AM, they sent me 2 quarts of RP 75w90. After reading online, I ordered 3 quarts of RP 75w140.
Now, I'm left wondering whether I should order another 3q of 140 to do the initial break in, and replace it with more 140 after 500 miles. Can I get away with doing the break in with the 90 weight and 140 afterwards?
There isn't really a "break-in" for gears when it comes to the oil, so there is no reason to wait for any certain number of miles. The correct oil weight is 75W-140, so just drain and refill with the correct oil weight when you have time.
When your car was brand new you didn't need to change the gear oil 500 miles later. Like the above have said, no need, just enjoy your new gears.
For what it's worth after installing my gears, I had an unrelated issued where I needed to change the gear oil about 1,000 miles after they were changed and there was no sign of metal in the oil when I drained it.