[D13]

So you have a light duty 1/2 ton (1" rotors) that has 3/4 ton springs in the back (should have had 3+1 or maybe 4+1 pack). Are you trying to make this a 3/4 ton? Because you don't have the frame or braking to manage constant heavy loading.
To answer your question, they should drop in, they will raise the front 1-2" depending on what spring is in it now, unless this has a 454 with A/C in which chase you probably wouldn't have those brakes. You will need an alignment after. You can also cut a coil to get back towards the stock ride height, and stiffer handling.

If you look at Rob's handling thread these springs are what he recommends to stiffen the handlig, albeit with cut coils.