I looked into this a while back. There are companies that sell bolt on adapters to make non-duallie trucks duallies, check out the following link:
http://www.southwestwheel.com/You may have to email them to see if they have the right conversion adapter for your bolt pattern.
These are pricey but compared to swapping the rear end and all the associated costs the adapter route would likely be a cost effective way to go.
But if you are wanting to actually use it for heavy duty hauling jobs a rear axle swap is probably the logical choice.
I hope this helps.
John
