Yes, it is for weight. On a standard closed tandem setup, it's good for a legal weight of 34000 pounds. With a spread, it's legal to 40000 pounds. Most modern spread setups have either or both, dump valve and lift axle. That prevents the dragging and damage to tires. But, a good driver knows how to drive with a spread axle trailer, so damage doesn't happen.
Thanks Gator and Brian. I'm hoping to get rest of the rear cut out and begin on the structure to support the tires. I'm gonna order the tires that will be for the Trophy Truck I'm building, so I can mount those in their location on this. I'm still undecided how much fabrication I want to do on this. Since the TT will be basically totally fabricated.