One trick I've heard of is to replace the rear shackle mounts with front shackle mounts from another donor. Should give a 3" to 4" drop, but with possibility of leaving very little room for the axle - better check it first.
Also, this will mess up the axle angle w.r.t. the driveshaft. You'll need some wedges to correct that.
Look at the shackle mount at the very front of the truck (mount #1, the front springs) - it actually sits inside the frame. I've seen folks move this to the rearmost shackle mount (mount #4, the rear springs), but it requires cutting the frame because it's too wide.
As for the middle mounts, the front spring mount (mount #2) is much shorter than the rear spring mount (mount #3). But where you need to mount it there are already lots of holes, so you might need re-enforcement or to fill the old holes.
I have spares of the shackle mounts from a '54 3/4 ton (same as 1/2 ton), and will send them for the cost of shipping if you decide to go this route. See ya,
-Boyo
