The internals from a four door 10 bolt will swap with the internals from a two door 10 bolt. You don't have to upgrade to the 14 bolt rear end if you're not really going to abuse it, i.e. Sudden throttle inputs, off-roading/shock loading.
If you found an axle that already has rotors in the rear I don't think that will affect the internals. You may have just gotten lucky. But if both your truck and the donor truck are GMT 400's I'd bet a dollar you're good.