That's what universal means. One size fits none
Your 2.5" single back will be sufficient. True duals that are two different lengths because they both have to run down the same side of the truck would seem to throw the balance off anyway because the back pressure will be different for each side.
I would go headers to a 2.5" Y pipe. 3" from the Y to a 3" inlet Muffler with dual 2.5" outlets and tailpipes. This will give you plenty of flow and both sides of the engine will be balanced.