'66 Barracuda rear axle question
The 7 1/4 does not have clips holging the axles at the diff, so thats easy. To remove the axle remove the wheel and drum. There is a large hole in the axle flange. Through it you will remove the 4 axle retaining nuts. Just rotate it around to access each one in turn.
Now the axle may slide right out or you may need a slide hammer to help as it most likely not been out in a very long time.
Once its out take it to a shop to remove and install the new bearing on a press. Replace the axle seal at this time and re-assemble.
I don't have the 66 Service Manual on a disk or I would post the procedure for you. If your new to the game you should consider picking up a factory manual. I know I refer back to it alot and I was an ASE Certified Tech.
I hope this helps.