Welcome to the Stovebolt Moll!
Four wheel drive was leafs in the front on all models until 1987 if I remember correctly. The independent front suspension four wheel drive starting in 1988 is torsion bar, not coil, on the 1/2-ton, 3/4-ton and 1-ton models.
I can't really see the emblems in the photos, does it say K20 or K30? The 20 would mean 3/4- and 30 1-ton. Also, the VIN number will tell you if its a 3/4-ton or 1-ton if you look it up.
Are you sure about the 12-bolt rear? That rear was used in cars and 1/2-ton pickups and I don't think was ever made in a floater version. If the truck has 3-lug hubs its probably not the rear that is commonly called a '12-bolt'.
