wanting ideas on building a body cart for 70-74 a bodies

what casters should i be looking for to use when building a car rack? 1000# each? I'm just not sure on casters. Do I want rubber, or hard plastic casters? Also, how big of square tubing should I use? where on the A-bodies is the best place to mount the 1/2 racks? I seen some built where they are separate and one goes in the front, while one mounts more towards the back. Any one have plans of how to build such a unit? just trying to get ideas, thanks guys!