What tools do you have now?
You will need a good inch lb. torque wrench as well as a good foot Lb. torque wrench, a adjustable spanner wrench,a good dial indicator with a good magnetic base and a ton of patience
AKA, buy a 1962 to 1969 Mopar factory Dodge or Plymouth service manual and read every part on how to work on their rear ends, the 7 1/4 inch ring gear rear ends all the way up to working on the Dana 60 rear ends as well as the 741 and 742 8 3/4 rear ends
The 1969 FSM for Dodge and Plymouth may have a section on how to set up the 489 cases also, depending on when the manual was printed, the 489 cases came out in mid year 1969.
On your deal with the 741 case you need to check the ring gear back lash in 4 different places, with a good dial indicator, 90 degrees apart, and write it down. Hopefully the four places are within .002 of each other on the backlash Once that is done you can remove the ring gear form the old center section, the opened rear end. Caution, all Mopar 8 3/4 rear ends have left handed threads on the ring gear bolts, all of them Don't strip or break one off loosening them up You will need to turn them clockwise facing them to loosen and counter clock wise to tighten them up Mopar recommends not reusing their stock ring gear bolts but I do. They come with a locking compound on the threads that was designed for one time use, I use blue Locktite on mine when I reuse them they need to be torque to 55 Ft lbs. You will need to mark both caps before removing them so they go back on the correct side that they where machine for
The FSM calls for no more than .0030 run out difference on the carrier and ring gear backlash, I've learned that I can heat up the ring gear to around 140 F in a oven or on my wood heating stove in the shop in the winter and then the ring gear will drop right on the carrier and sit flatter than trying to pull the ring gear down with the ring gear bolts with the ring gear at room temperature, below 70 F
I need to go eat dinner now so get the tools and FSM and let me know later when your ready to try this, their are several other torque specs you need to know about as well as some other things you don't need to worry about, such as pinion gear depth and pinion bearing preload on your deal now