Axles swap directly from 1/2 and 3/4 ton pickups up to '87, and blazer/suburban up to '91 into any 1/2 and 3/4 tons back to 73. The only perch spacing difference you'll find is for the 1tons. I have been lucky and gotten a K20 and K35 that are both 4.56 factory gears, but the K20 has a Gov-lok.