changed gears in a 741 now have a whine

There are a few things to got right all at once to make it silent.
The pinion depth needs to be right. Not "close" but within a thou or so max. if you need the right shims to do this, get them.
The rotating torque figure needs to be right.
The backlash needs to be within spec. I thought they use .008-.010" but it's been a little while. There is enough resistance just by putting pressure on the carrier with a gloved hand while you turn the pinion to make the pattern look right.
Once those are right, you need to follow the proper break in procedure which is easy but you can't rush it.
step 1 - put car on jackstands with rear installed and oil level full. Start vehicle, and carefully bring it up to about 30mph in drive on the stands, and keep it there for 15 minutes. Then shut it off get it off the stands, and let it cool overnight.
Step 2 - Once fully cold, drive vehicle very lightly for about 5 miles. Do not beat on it at all. Just light driving, smooth light accel and decel. then park and let it cool fully again. Step 3- Once cool, take it out and wail on it and listen for noises.

You must give new gears a chance to seat to each other before they get really driven hard.