I take it that you are talking about the 1951 GMC that is listed in your signature.
Six lug wheels indicate 1/2 ton, eight lug usually mean 3/4 ton and one tons usually have larger heavy duty rims. One ton pickups with a box had the 9-1/2 or so foot beds and most ran flat beds with dual rear wheels.
Here is a link to another website that has some info that you might be able to use
http://www.oldgmctrucks.com/index.html It looks like an interesting site for anyone with an AD GMC truck.