I would swap the one out of your old case.
If not Transtar should be able to hook you up. I know they have a place in I think Merrimack N.H. Pretty sure they have other locations around the country.
Just a thought, if your going to tear the new case all apart to swap the input, you might as well rebuild it with new bearings, bushings, & chain.
If your going to do that, why not rebuild the one that's in your truck?