I just replaced my front and rear springs on my 51. Don’t lift your rearend and put jackstands under it. Allow your leaves to be in a relaxed position and then put jackstands under it. If you have your springs loaded, you will get a little support when they rapidly move to a relaxed position. I had minimal flex on mine a I got away quickly laughing at my stupidity!

As others have said, front pivot hanger is threaded (not the bushing) and the shackle portion has a threaded bushing.

I found it easier to remove everything with zerk fittings removed.

Chris