Go to my web site www.droppedaxles.com then to Tech Articles. Here is a address to the page http://droppedaxles.com/TECH_ARTICLES.html
Read the spindle article. The 1/2 ton axle will bolt right into the 3/4 ton Chevy. Some GMC 3/4 tons have 2" wide springs and the 1/2 ton has 1-3/4" wide springs. This is a easy fix by moving the holes out with a die grinder by 1/8" each. The 3/4 ton axle has bigger ID king pins than the 1/2 ton. The 3/4 ton spindles have bigger ID bearings than the 1/2 ton. You can use the 49-54 Chevy car backing plates and drums on the 1/2 ton spindles. This will get you the 5 bolt pattern Chevy car wheels (5 on 4-3/4" pattern)