I need to know whether a dually and standard rear-end are interchangeable besides I'm assuming longer studs. There shouldn't be any difference between axle length brake location etc. right????????

My dually has a wide track option for an 8' wide body. I believe regular duallies are still different than single wheel trucks.
FYI in your truck description you list CCSB. If you were to order a CC truck they would give you a Cab & Chassis truck not a Crew Cab.