A 1 ton rear axle from the 80's models will bolt in as far as spring perch width goes (1 ton is narrower than a 3/4 ton). One thing to keep in mind when putting ANY 3/4 ton or 1 ton rear axle in your 1/2 ton is the axle tubes of the heavier axles will be of a larger diameter than your factory 12 bolt rear. This isn't the end of the world, but you will need to buy/build new spring plates and U bolts.
This is a great way to go.