New 66 C10 project suspension trouble?

[Mikes66ChevyC10]

So tonight I put the truck up on Jack stands in order to remove the bolts holding the bed on the frame as some friends are coming over tomorrow to help take the bed off. When I got under the truck I noticed a potential problem. The pass side Rear wheel is rubbing the inside of the bed and the drivers side has plenty of room. Looks to be about a 3/4 inch difference between the pass side and the drivers side. What could be causing this? Should I be worried? I also found that the truck has a one piece driveshaft and where it passes through the cross member it is not centered.