You should be able to use the axles front and rear from the '73-'87 K/V20 or '77-'91 K/V30. Use caution when looking the mid '80s K/V20, some of them used the 9.5" ring gear 14 bolt, which is a semi float light duty. Ideally, the K/V30 axles woild be best combo for overall strength, as they are a Dana 60 front/ GM 14 bolt full float rear (some used a Dana 70 in the rear, usually duallies and tow truck package). The 3/4 tons used the same rear, but wiht a Dana 44 up front, simlar to what you already have but with open knuckles and disk brakes. Going to either front axle will gain you a tighter turning radius in addition to the disk brakes. You woul need to swap to a dual circuit master cylinder, preferrably with power assist, if you use the disk brake axle.
If you only want to swap the rear end, the 14 bolt from the years mentioned will do, wouldn't have to be from a 4x4, 2wd will be fine. You will want to consider swapping gears in the front to match, which shouldn't be a problem as they are still available fro the front diff.
