With all due respect to the 19. 5" wheels and tires, nothing will gain stability like an extra set of wheels. The increased track of adding dual rear wheels is in no way the same as having 19. 5" wheels and tires. If it was me, and I was in your position wanting to run dual wheels on a 2500, I would go with what is proven and has no doubts about it tract record. I would go to Dodge for the rear fenders, front wheel adapters, and clearance lights. They work and they work well, why mess with anything but the best? For the proper wheels Southwest Wheel has both Alcoa aluminum wheels and steel replacement wheels. Both or a combination of the two will work without regret, or worry.
I hope you take the time to plan this move carefully, if done right you will have a unique and functional truck that performs as you would like. Take the short way around and the outcome may not be as desirable. Good luck.