[lolife99]

The '80 rearend will have different shock mounting points.
You may have to remove the shock mounts off the 3/4-ton rearend and weld them to the '80 1/2-ton rearend.
You will need to bend up a few new steel brake lines as well.
Alot of people before you have done this swap.
So it's nothing new.

If I were you,...
I would install a set of ECE's (3/4 to 1/2 ton) conversion spindles.
They bolt right on your 3/4 ton front end.
Swap nothing else.
They allow you to use 1/2 ton rotors and calipers.
Simple for what you are wanting to do.
Are you lowering it as well?